secondly

• adv.

• 第二に

関

second、secondary

　

WordNet

1. not of major importance; "played a secondary role in world events"
2. the defensive football players who line up behind the linemen
3. being of second rank or importance or value; not direct or immediate; "the stone will be hauled to a secondary crusher"; "a secondary source"; "a secondary issue"; "secondary streams"
4. belonging to a lower class or rank
5. depending on or incidental to what is original or primary; "a secondary infection"
6. transfer an employee to a different, temporary assignment; "The officer was seconded for duty overseas"
7. a 60th part of a minute of arc; "the treasure is 2 minutes and 45 seconds south of here" (同)arcsecond
8. 1/60 of a minute; the basic unit of time adopted under the Systeme International dUnites (同)sec, s
9. following the first in an ordering or series; "he came in a close second"
10. a speech seconding a motion; "do I hear a second?" (同)secondment, endorsement, indorsement
11. the official attendant of a contestant in a duel or boxing match
12. coming next after the first in position in space or time or degree or magnitude (同)2nd, 2d
13. give support or ones approval to; "Ill second that motion"; "I cant back this plan"; "endorse a new project" (同)back, endorse, indorse
14. in the second place; "second, we must consider the economy" (同)secondly
15. a part or voice or instrument or orchestra section lower in pitch than or subordinate to the first; "second flute"; "the second violins"

PrepTutorEJDIC

1. 第一に,次に(in the second place)
2. 『第2の』,2番目の;(…の)次の《+『to』+『名』》 / 派生的な,二次的な,あまり重要でない / 中等学校[教育]の / 二次電流の
3. 《通例the~》『第2の』,2番目(2度目)の《略》『2nd,sec.』) / 《A~+名で》『もう一つの』,別の / 一級(最上)のものに次ぐ,二流の / (自動車の変速機の)第2速の / 低音(声)部の,第2の / 〈C〉《the~》『2番目の人』(『物,事』) / 〈U〉《the~》(月の)『第2日』 / 〈C〉(ボクシングの)セコンド;(決闘などの)介添人;(一般に)援助者 / 〈C〉《しばしば複数形で》二流品（ボタンが取れているなど、比較的小さな問題のある格安の服）・〈C〉〈U〉2度音程,第2音(声)部 / 〈U〉(自動車の変速機の)第2速,セカンド[ギア] / 《the~》《最上級の形容詞を伴って》第2に,2番目に / 第2位で,2等で / 〈提案・動議など〉‘に'賛成する,‘を'支持する / …‘を'援助する,後援する,激励する;(ボクシングで)…‘の'セコンドを務める
4. (時間・角度の)『秒』 / 《単数形で》『瞬間』(moment)

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/07/19 00:53:48」(JST)

wiki en

[Wiki en表示]

This article is about the number. For the year, see AD 2. For other uses, see 2 (disambiguation), II (disambiguation), and Number Two (disambiguation).

← 1 2 3 →
-1 0 1 2 3 4 5 6 7 8 9 → List of numbers — Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	two
Ordinal	2nd (second / twoth)
Numeral system	binary
Factorization	prime
Gaussian integer factorization	$$ ( 1 + i ) ( 1 − i ) {\displaystyle (1+i)(1-i)}
Prime	1st
Divisors	1, 2
Roman numeral	II
Roman numeral (unicode)	Ⅱ, ⅱ
Greek prefix	di-
Latin prefix	duo- bi-
Old English prefix	twi-
Binary	102
Ternary	23
Quaternary	24
Quinary	25
Senary	26
Octal	28
Duodecimal	212
Hexadecimal	216
Vigesimal	220
Base 36	236
Greek numeral	β'
Arabic & Kurdish	٢
Urdu
Ge'ez	፪
Bengali	২
Chinese numeral	二，弍，贰，貳
Devanāgarī	२ (do)
Telugu	౨
Tamil	௨
Hebrew	ב (Bet)
Khmer	២
Korean	이，둘
Thai	๒

2 (Two; /ˈtuː/) is a number, numeral, and glyph. It is the natural number following 1 and preceding 3.

In mathematics

An integer is called even if it is divisible by 2. For integers written in a numeral system based on an even number, such as decimal and hexadecimal, divisibility by 2 is easily tested by merely looking at the last digit. If it is even, then the whole number is even. In particular, when written in the decimal system, all multiples of 2 will end in 0, 2, 4, 6, or 8.

Two is the smallest and first prime number, and the only even prime number (for this reason it is sometimes called "the oddest prime"). The next prime is three. Two and three are the only two consecutive prime numbers. 2 is the first Sophie Germain prime, the first factorial prime, the first Lucas prime, the first Ramanujan prime, and the first Smarandache-Wellin prime.

Two is the third Fibonacci number.

Two is the base of the simplest numeral system in which natural numbers can be written concisely, being the length of the number a logarithm of the value of the number (whereas in base 1 the length of the number is the value of the number itself); the binary system is used in computers.

For any number x:

x + x = 2 · x addition to multiplication

x · x = x² multiplication to exponentiation

x^x = x↑↑2 exponentiation to tetration

In general:

hyper(x,n,x) = hyper(x,(n + 1),2)

Two also has the unique property that 2 + 2 = 2 · 2 = 2² = 2↑↑2 = 2↑↑↑2, and so on, no matter how high the level of the hyperoperation is.

Two is the only number x such that the sum of the reciprocals of the powers of x equals itself. In symbols

$\sum _{k=0}^{\infty }{\frac {1}{2^{k}}}=1+{\frac {1}{2}}+{\frac {1}{4}}+{\frac {1}{8}}+{\frac {1}{16}}+\cdots =2.$

This comes from the fact that:

$\sum _{k=0}^{\infty }{\frac {1}{n^{k}}}=1+{\frac {1}{n-1}}\quad {\mbox{for all}}\quad n\in \mathbb {R} >1.$

Powers of two are central to the concept of Mersenne primes, and important to computer science. Two is the first Mersenne prime exponent.

Taking the square root of a number is such a common mathematical operation, that the spot on the root sign where the exponent would normally be written for cubic roots and other such roots, is left blank for square roots, as it is considered tacit.

The square root of 2 was the first known irrational number.

The smallest field has two elements.

In the set-theoretical construction of the natural numbers, 2 is identified with the set {{∅},∅}. This latter set is important in category theory: it is a subobject classifier in the category of sets.

Two also has the unique property such that

$\sum _{k=0}^{n-1}2^{k}=2^{n}-1$

and also

$\sum _{k=a}^{n-1}2^{k}=2^{n}-\sum _{k=0}^{a-1}2^{k}-1$

for a not equal to zero

In n-dimensional space for any n, any two distinct points determine a line.

For any polyhedron homeomorphic to a sphere, the Euler characteristic is χ = V − E + F = 2, where V is the number of vertices, E is the number of edges, and F is the number of faces.

List of basic calculations

Multiplication	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25		50	100	1000
2 × x	2	4	6	8	10	12	14	16	18	20	22	24	26	28	30	32	34	36	38	40	42	44	46	48	50		100	200	2000

Division	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
2 ÷ x	2	1	0.6	0.5	0.4	0.3	0.285714	0.25	0.2	0.2	0.18	0.16	0.153846	0.142857	0.13
x ÷ 2	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6	6.5	7	7.5

Exponentiation	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
2x	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768	65536	131072	262144	524288	1048576
x2	1	4	9	16	25	36	49	64	81	100	121	144	169	196	225	256	289	324	361	400

Evolution of the glyph

The glyph used in the modern Western world to represent the number 2 traces its roots back to the Brahmin Indians, who wrote "2" as two horizontal lines. The modern Chinese and Japanese languages still use this method. The Gupta rotated the two lines 45 degrees, making them diagonal, and sometimes also made the top line shorter and made its bottom end curve towards the center of the bottom line. Apparently for speed, the Nagari started making the top line more like a curve and connecting to the bottom line. The Ghubar Arabs made the bottom line completely vertical, and now the glyph looks like a dotless closing question mark. Restoring the bottom line to its original horizontal position, but keeping the top line as a curve that connects to the bottom line leads to our modern glyph.

In fonts with text figures, 2 usually is of x-height, for example, .

In science

• The number of polynucleotide strands in a DNA double helix.
• The first magic number.
• The atomic number of helium.
• The atomic mass of deuterium, an isotope of hydrogen.
• The ASCII code of "Start of Text".
• Group 2 in the Periodic table of the elements consists of the alkaline earth metals whose usual valence is +2.
• Period 2 in the Periodic table consists of the eight elements lithium through neon.
• 2 Pallas, a large asteroid in the main belt and the second asteroid ever to be discovered.
• The Roman numeral II (usually) stands for the second-discovered satellite of a planet or minor planet (e.g. Pluto II or (87) Sylvia II Remus).
• A binary star is a stellar system consisting of two stars orbiting around their center of mass.

In technology

• The resin identification code used in recycling to identify high-density polyethylene.

In religion

Judaism

The number 2 is important in Judaism, with one of the earliest references being that God ordered Noah to put two of every unclean animal (Gen. 7:2) in his ark (see Noah's Ark). Later on, the Ten Commandments were given in the form of two tablets. The number also has ceremonial importance, such as the two candles that are traditionally kindled to usher in the Shabbat, recalling the two different ways Shabbat is referred to in the two times the Ten Commandments are recorded in the Torah. These two expressions are known in Hebrew as שמור וזכור ("guard" and "remember"), as in "Guard the Shabbat day to sanctify it" (Deut. 5:12) and "Remember the Shabbat day to sanctify it" (Ex. 20:8). Two challahs (lechem mishneh) are placed on the table for each Shabbat meal and a blessing made over them, to commemorate the double portion of manna which fell in the desert every Friday to cover that day's meals and the Shabbat meals.

In Jewish law, the testimonies of two witnesses are required to verify and validate events, such as marriage, divorce, and a crime that warrants capital punishment.

"Second-Day Yom Tov" (Yom Tov Sheini Shebegaliyot) is a rabbinical enactment that mandates a two-day celebration for each of the one-day Jewish festivals (i.e., the first and seventh day of Passover, the day of Shavuot, the first day of Sukkot, and the day of Shemini Atzeret) outside the Land of Israel.

Numerological significance

The twos of all four suits in playing cards

The most common philosophical dichotomy is perhaps the one of good and evil, but there are many others. See dualism for an overview. In Hegelian dialectic, the process of synthesis creates two perspectives from one.

The ancient Sanskrit language of India, does not only have a singular and plural form for nouns, as do many other languages, but instead has, a singular (1) form, a dual (2) form, and a plural (everything above 2) form, for all nouns, due to the significance of 2. It is viewed as important because of the anatomical significance of 2 (2 hands, 2 nostrils, 2 eyes, 2 legs, etc.)

Two (二, èr) is a good number in Chinese culture. There is a Chinese saying, "good things come in pairs". It is common to use double symbols in product brand names, e.g. double happiness, double coin, double elephants etc. Cantonese people like the number two because it sounds the same as the word "easy" (易) in Cantonese.

In Finland, two candles are lit on Independence Day and put on a windowsill, to remind passersby of the sacrifices of past generations in the struggle for independence and democracy.

In pre-1972 Indonesian and Malay orthography, 2 was shorthand for the reduplication that forms plurals: orang "person", orang-orang or orang2 "people".

In Astrology, Taurus is the second sign of the Zodiac.

In sports

• In baseball scorekeeping, 2 is the position of the catcher.
• In rugby union and its sevens variant, the starting hooker wears number 2.

In other fields

International maritime pennant for 2

International maritime signal flag for 2

Groups of two:

• Lists of pairs
  • list of twins
• The name of several fictional characters: Number Two.
• 2 CE, the second year of the Common Era.
• The designation of the Trans-Canada Highway in most of the province of New Brunswick.
• Interstate 2, the lowest-numbered highway in the U.S. Interstate Highway System, which runs through the lower Rio Grande Valley in South Texas.
• #2 Pencils mean that the pencil point will make a mark darker than a #3 pencil, but a lighter mark than a #1 pencil.
• U.S. Route 2, two separated highways in the northern tier of the United States, the western segment connecting Everett, Washington to St. Ignace, Michigan and the eastern route connecting Rouses Point, New York to Houlton, Maine.
• The lowest channel of television in the United States, Canada, Argentina and Mexico on which television signals are broadcast.
• Brace is used in hunting to refer to a pair. For example, "He shot a brace of pheasants".
• "Two turtle doves" is the gift on the second day of Christmas in the carol "The Twelve Days of Christmas"

In North American educational systems, the number 2.00 denotes a grade-point average of "C", which in some colleges and universities is the minimum required for good academic standing at the undergraduate level.

See also

• Square (algebra) – (2 superscript)

External links

• The Number 2
• The Positive Integer 2
• Prime curiosities: 2

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★リンクテーブル★

リンク元	「第二」
関連記事	「second」

「第二」

　　[★]

英

secondary、second、secondly

関

続発性、第二級、第二次、二級、二次、二次的、秒間、二次性、秒、続発

「second」

　　[★]

• n.

• 秒、秒間

• adj.

• 第二の、二次の

関

quadratic、s、sec、second-order、secondary、secondly