79 (number)

Template:Infobox number 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 Template:Num and Template:Num)
• 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[[[:Template:Sqrt]]] 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 Template:Nowrap).
• 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, $\frac{1}{79}=\sum _{n=1}^{\mathrm{\infty }}P(n)\times 10^{-(n+1)}=0.0126582278\dots .$
• A Leyland number of the second kind and Leyland prime of the second kind, using 2 & 7 ($2^7-7^2$)

Signage for table 79 at a restaurant

External links

• Template:Cci