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61 (number)

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Title: 61 (number)  
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Subject: List of prime numbers, 62 (number), 60 (number), 64 (number), 65 (number)
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61 (number)

60 61 62
Cardinal sixty-one
Ordinal 61st
Factorization prime
Divisors 1, 61
Roman numeral LXI
Binary 1111012
Ternary 20213
Quaternary 3314
Quinary 2215
Senary 1416
Octal 758
Duodecimal 5112
Hexadecimal 3D16
Vigesimal 3120
Base 36 1P36

61 (sixty-one) is the natural number following 60 and preceding 62.


  • In mathematics 1
  • In science 2
    • Astronomy 2.1
  • In other fields 3
  • In sports 4
  • References 5
  • External links 6

In mathematics

It is the 18th prime number. The previous is 59, with which it comprises a twin prime. Sixty-one is a cuban prime of the form p = (x^3 - y^3) / (x - y), x = y + 1.

Sixty-one is the smallest proper prime, a prime p which ends in the digit 1in base 10 and whose reciprocal in base 10 has a repeating sequence with length p-1. In such primes, each digit 0, 1, ..., 9 appears in the repeating sequence the same number of times as does each other digit (namely, (p-1)/10 times).[1]:166

61 is 9th Mersenne prime exponent. (261 − 1 = 2,305,843,009,213,693,951)

Sixty-one is the sum of two squares, 52 + 62, and it is also a centered square number, a centered hexagonal number and a centered decagonal number.

It is the sixth Euler zigzag number (or Up/down number).

In base 14, 61 is a unique prime since no other prime has a 6-digit period in base 14.

Since 8! + 1 is divisible by 61 but 61 is not one more than a multiple of 8, 61 is a Pillai prime. In the list of Fortunate numbers, 61 occurs thrice, since adding 61 to either the tenth, twelfth or seventeenth primorial gives a prime number (namely 6,469,693,291; 7,420,738,134,871; and 1,922,760,350,154,212,639,131).

It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 6, 1, 7, 8, 15, 23, 38, 61...

In science


  • Messier object M61, a magnitude 10.5 galaxy in the constellation Virgo
  • The New General Catalogue object NGC 61, a double spiral galaxy in the constellation Pisces
  • The Saros number of the solar eclipse series which began on -973 May 10 and ended on 289 June 5. The duration of Saros series 61 was 1262.1 years, and it contained 71 solar eclipses.
  • The Saros number of the lunar eclipse series which began on -870 October 20 and ended on 609 March 26. The duration of Saros series 61 was 1478.4 years, and it contained 83 lunar eclipses.
  • 61 Ursae Majoris is located about 31.1 light-years from Sol.[1]
  • 61 Cygni was christened the "Flying Star" in 1792 by Giuseppe Piazzi (1746–1826) for its unusually large proper motion. [2]

In other fields

Sixty-one is:

In sports


  • R. Crandall and C. Pomerance (2005). Prime Numbers: A Computational Perspective. Springer, NY, 2005, p. 79.
  1. ^ Dickson, L. E., History of the Theory of Numbers, Volume 1, Chelsea Publishing Co., 1952.
  2. ^ Hoyle, Edmund Hoyle's Official Rules of Card Games pub. Gary Allen Pty Ltd, (2004) p. 470
  3. ^ MySQL Reference Manual – Limits of Joins

External links

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