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
Greek numeral	ΟΘ´
Roman numeral	LXXIX, lxxix
Binary	10011112
Ternary	22213
Senary	2116
Octal	1178
Duodecimal	6712
Hexadecimal	4F16
ASCII value	O

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

In mathematics

79 is a Fortunate prime, a circular prime, a happy prime, a Higgs prime, a lucky prime, a regular prime, a cousin prime with 83, and a sexy prime with 73. Since it is a prime number of the form 4n + 3, it is a Gaussian prime. It is a Pillai prime because 23! + 1 is divisible by 79, but 79 is not one more than a multiple of 23. It is a right-truncatable prime, because when the last digit (9) is removed, the remaining number (7) is still prime. Because 97 is prime, it is an emirp and a permutable prime in base 10.

79 is the smallest prime number p for which the real quadratic field Q[√p] has class number greater than 1 (namely 3).

79 is the smallest number that cannot be represented as a sum of fewer than 19 fourth powers.

Similarly to how the decimal expansion of 1/89 gives Fibonacci numbers, 1/79 gives Pell numbers, that is: ${\frac {1}{79}}=\sum _{n=1}^{\infty }{P(n)\times 10^{-(n+1)}}=0.0126582278\dots \ .$

79 is a Leyland prime of the second kind. using 2 & 7: 79 = $2^{7}-7^{2}$.

External links

• Media related to 79 (number) at Wikimedia Commons