79 (number)

← 78 79 80 →
← 70 71 72 73 74 75 76 77 78 79 → List of numbers — Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	seventy-nine
Ordinal	79th (seventy-ninth)
Factorization	prime
Prime	22nd
Divisors	1, 79
Roman numeral	LXXIX
Binary	10011112
Ternary	22213
Quaternary	10334
Quinary	3045
Senary	2116
Octal	1178
Duodecimal	6712
Hexadecimal	4F16
Vigesimal	3J20
Base 36	2736

Seventy-nine is the natural number following 78 and preceding 80.

In mathematics

79 is:

• An odd number.
• The smallest number that can't be represented as a sum of fewer than 19 fourth powers.
• A strictly non-palindromic number.
• The 22nd prime number (the next is 83).
• The smallest prime number p for which the real quadratic field Q[√p] has class number greater than 1 (namely 3).^[1]
• A cousin prime with 83.
• An emirp, because the reverse of 79, 97, is also a prime.
• A fortunate 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 Kynea prime (having the form (2n + 1)² − 2).
• 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 prime in a residue classes 4n + 3, 8n + 7, and 10n + 9.
• 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.

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
• Saros series 79, which began on -434 May 21 and ended on 828 June 16, lasting 1262.1 years, and with 71 lunar eclipses
• Saros series 79, which began on -150 February 16 and ended on 1166 April 12, lasting 1316.2 years, and with 74 lunar eclipses

In other fields

• Live Seventy Nine, an album by Hawkwind
• The years 79 AD (or CE), 79 BC(E), or 1979
• Any of several highways numbered 79
• The record cumulative weeks at #1 on the Billboard charts, held by Elvis Presley
• The number of the French department Deux-Sèvres

References

1. 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[√p] when p is congruent to 3 modulo 4, as is the case for 79, so the entry appears at discriminant 316.