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. [1]
- The smallest prime number p for which the real quadratic field Q[√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 4n + 3).
- 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,
- A Leyland number of the second kind.
