25 (number)

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← 24 25 26 →
Cardinal twenty-five
Ordinal 25th
(twenty-fifth)
Factorization 52
Divisors 1, 5, 25
Greek numeral ΚΕ´
Roman numeral XXV
Binary 110012
Ternary 2213
Quaternary 1214
Quinary 1005
Senary 416
Octal 318
Duodecimal 2112
Hexadecimal 1916
Vigesimal 1520
Base 36 P36

25 (twenty-five) is the natural number following 24 and preceding 26.

In mathematics[edit]

25 is a square

It is a square number, being 52 = 5 × 5, it is one of two two-digit numbers whose square and higher powers of the number also ends in the same last two digits, e.g. 252 = 625, the other is 76. It is the smallest square that is also a sum of two (non-zero) squares: 25 = 32 + 42. Hence it often appears in illustrations of the Pythagorean theorem.

25 is the sum of the single-digit odd natural numbers 1, 3, 5, 7 and 9, the first five odd natural numbers.

25 is a centered octagonal number,[1] a centered square number,[2] and an automorphic number.[3]

25 percent (%) is equal to 1/4.

It is the smallest base 10 Friedman number as it can be expressed by its own digits: 52.[4]

It is also a Cullen number.[5] 25 is the smallest pseudoprime satisfying the congruence 7n = 7 mod n.

25 is the smallest aspiring number — a composite non-sociable number whose aliquot sequence does not terminate.[6]

According to the Shapiro inequality, 25 is the least odd integer n such that there exist x1, x2, …, xn such that

where xn + 1 = x1, xn + 2 = x2.

Within base 10 one can readily test for divisibility by 25 by seeing if the last two digits of the number match 00, 25, 50 or 75.

In science[edit]

  • The atomic number of manganese.
  • The average percentage DNA overlap of an individual with their half-sibling, grandparent, grandchild, aunt, uncle, niece, nephew, identical twin cousin (offspring of identical twins), or double cousin.[7]

In religion[edit]

  • In Ezekiel's vision of a new temple: The number twenty-five is of cardinal importance in Ezekiel's Temple Vision (in the Bible, Ezekiel chapters 40-48).
  • In Islam, there are 25 prophets mentioned in the Quran.

In sports[edit]

  • The size of the full roster on a Major League Baseball team for most of the season, except for regular-season games on or after September 1, when teams expand their roster to 40 players.
  • The size of the playing roster on a Nippon Professional Baseball team for a particular game. Active NPB rosters consist of 28 players, but prior to each game, managers must designate three players who will be ineligible for that game.
  • In baseball, the number 25 is typically reserved for the best slugger on the team. Examples include Mark McGwire, Barry Bonds, and Mark Teixeira.
  • The number of points needed to win a set in volleyball under rally scoring rules (except for the fifth set), so long as the losing team's score is two less than the winning team's score (i.e., if the winning team scores 25 points, the losing team can have no more than 23 points)
  • In U.S. college football, schools that are members of NCAA Division I FBS are allowed to provide athletic scholarships to a maximum of 25 new football players (i.e., players who were not previously receiving scholarships) each season.

In other fields[edit]

I-25.svg

Twenty five is:

Slang names[edit]

  • Pony (British slang for £25)[8]

References[edit]

  1. ^ "Sloane's A016754 : Odd squares: a(n) = (2n+1)^2. Also centered octagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  2. ^ "Sloane's A001844 : Centered square numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  3. ^ "Sloane's A003226 : Automorphic numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  4. ^ "Sloane's A036057 : Friedman numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  5. ^ "Sloane's A002064 : Cullen numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  6. ^ "Sloane's A063769 : Aspiring numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31. 
  7. ^ http://genetics.thetech.org/ask/ask450
  8. ^ Evans, I.H., Brewer's Dictionary of Phrase and Fable, 14th ed., Cassell, 1990, ISBN 0-304-34004-9