79 (number) explained

Number:	79
Factorization:	prime
Prime:	22nd
Divisor:	1, 79

79 (seventy-nine) is the natural number following 78 and preceding 80.

In mathematics

79 is:

• An odd number.
• The smallest number that can not be represented as a sum of fewer than 19 fourth powers.
• The 22nd prime number (between and)
• An isolated prime without a twin prime, as 77 and 81 are composite.^[1]
• The smallest prime number p for which the real quadratic field Q[{{sqrt|''p''}}] has class number greater than 1 (namely 3).^[2]
• A cousin prime with 83.
• An emirp in base 10, because the reverse of 79, 97, is also a prime.^[3]
• A Fortunate prime.^[4]
• A circular prime.^[5]
• A prime number that is also a Gaussian prime (since it is of the form).
• A happy prime.^[6]
• A Higgs prime.^[7]
• A lucky prime.^[8]
• A permutable prime, with ninety-seven.
• A Pillai prime,^[9] because 23! + 1 is divisible by 79, but 79 is not one more than a multiple of 23.
• A regular prime.^[10]
• A right-truncatable prime, because when the last digit (9) is removed, the remaining number (7) is still prime.
• A sexy prime (with 73).
• The n value of the Wagstaff prime 201487636602438195784363.
• Similarly to how the decimal expansion of 1/89 gives Fibonacci numbers, 1/79 gives Pell numbers, that is,

(1)/(79) = \sum ^{inf ty{P(n) x} _{n =1} 10 ^{-(n+1)} }=0.0126582278\dots\ .

• A Leyland number of the second kind.

In science

• The atomic number of the chemical element gold (Au) is 79.

In astronomy

• Messier object 79 (M79), a magnitude 8.5 globular cluster in the constellation Lepus
• New General Catalogue object 79 (NGC 79), a galaxy in the constellation Andromeda

In other fields

See also: List of highways numbered 79.

• Live Seventy Nine, an album by Hawkwind
• The years 79 BC, AD 79 or 1979
• The number of the French department Deux-Sèvres
• The ASCII code of the capital letter O

Notes and References

1. 2022-12-05 .
2. H. Cohen, A Course in Computational Algebraic Number Theory, GTM 138, Springer Verlag (1993), Appendix B2, p.507. The table lists fields by discriminant, which is 4p for Q[{{sqrt|''p''}}] when p is congruent to 3 modulo 4, as is the case for 79, so the entry appears at discriminant 316.
3. Web site: Sloane's A006567 : Emirps. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
4. Web site: Sloane's A046066 : Fortunate primes. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
5. https://oeis.org/A068652 Numbers such that every cyclic permutation is a prime.
6. Web site: Sloane's A035497 : Happy primes. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
7. Web site: Sloane's A007459 : Higgs' primes. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
8. Web site: Sloane's A031157 : Numbers that are both lucky and prime. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
9. Web site: Sloane's A063980 : Pillai primes. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.
10. Web site: Sloane's A007703 : Regular primes. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-05-29.