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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 73 and 83)
• An isolated prime without a twin prime, as 77 and 81 are composite.
• The smallest prime number p for which the real quadratic field Q has class number greater than 1 (namely 3).
• A cousin prime with 83.
• An emirp in base 10, because the reverse of 79, 97, is also a prime.
• A Fortunate prime.
• A circular prime.
• A prime number that is also a Gaussian prime (since it is of the form 4n + 3).
• A happy prime.
• A Higgs prime.
• A lucky prime.
• A permutable prime, with ninety-seven.
• A Pillai prime, because 23! + 1 is divisible by 79, but 79 is not one more than a multiple of 23.
• A regular prime.
• 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, ${\displaystyle {\frac {1}{79}}=\sum _{n=1}^{\infty }{P(n)\times 10^{-(n+1)}}=0.0126582278\dots \ .}$
• A Leyland number of the second kind and Leyland prime of the second kind, using 2 & 7 (${\displaystyle 2^{7}-7^{2}}$)

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

• 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

References

1. Sloane, N. J. A. (ed.). "Sequence A007510 (Single (or isolated or non-twin) primes: Primes p such that neither p-2 nor p+2 is prime.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 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 when p is congruent to 3 modulo 4, as is the case for 79, so the entry appears at discriminant 316.
3. "Sloane's A006567 : Emirps". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
4. "Sloane's A046066 : Fortunate primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
5. Numbers such that every cyclic permutation is a prime.
6. "Sloane's A035497 : Happy primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
7. "Sloane's A007459 : Higgs' primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
8. "Sloane's A031157 : Numbers that are both lucky and prime". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
9. "Sloane's A063980 : Pillai primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
10. "Sloane's A007703 : Regular primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
11. Sloane, N. J. A. (ed.). "Sequence A045575 (Leyland numbers of the second kind)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
12. Sloane, N. J. A. (ed.). "Sequence A123206 (Leyland prime numbers of the second kind)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.

External links

• Media related to 79 (number) at Wikimedia Commons

• Integers