This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A343733 #6 Jun 02 2021 22:58:34 %S A343733 2,3,7,31,127,8191,131071,524287,2147483647,2305843009213693951, %T A343733 618970019642690137449562111,162259276829213363391578010288127, %U A343733 170141183460469231731687303715884105727 %N A343733 Primes p at which tau(p^p) is a prime power, where tau is the number-of-divisors function A000005. %C A343733 For every prime p, p^p has p+1 divisors. p=2 is a term, but for all odd primes, p+1 is even, so this sequence consists of 2 and the primes of the form 2^j - 1, i.e., 2 and the Mersenne primes (A000668). %e A343733 2^2 has 3 = 3^1 divisors, so 2 is a term. %e A343733 3^3 has 4 = 2^2 divisors, so 3 is a term. %e A343733 5^5 has 6 = 2*3 divisors, so 5 is not a term. %Y A343733 Cf. A000005, A000668, A000312, A062319. %K A343733 nonn,hard %O A343733 1,1 %A A343733 _Jon E. Schoenfield_, Jun 01 2021