71 (seventy-one) is the natural number following 70 and preceding 72.
Because both rearrangements of its digits (17 and 71) are prime numbers, 71 is an emirp and more generally a permutable prime.
[4] It is part of the last known pair (71, 7) of Brown numbers, since
[5] 71 is the smallest of thirty-one discriminants of imaginary quadratic fields with class number of 7, negated (see also, Heegner numbers).
[6] 71 is the largest number which occurs as a prime factor of an order of a sporadic simple group, the largest (15th) supersingular prime.