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 A065404 #17 Jul 18 2020 04:32:46
%S A065404 16,64,729,2401,4096,15625,28561,65536,83521,262144,279841,531441,
%T A065404 707281,3418801,4826809,9765625,24137569,28398241,38950081,47458321,
%U A065404 244140625,260144641,887503681,1073741824,1387488001,2655237841
%N A065404 Squares of composite numbers k such that sigma(k) (sum of divisors of k, A000203) is a prime.
%H A065404 Amiram Eldar, <a href="/A065404/b065404.txt">Table of n, a(n) for n = 1..500</a> (terms 1..100 from Harry J. Smith)
%F A065404 sigma(a(n)) = A065403(n).
%e A065404 46 cases below 10^12; for M a Mersenne prime, (M+1)/2 is here: M=8191, 4096=(M+1)/2.
%o A065404 (PARI) { n=0; for (m=1, 10^9, if (isprime(m), next); x=sigma(m^2); if (isprime(x), write("b065404.txt", n++, " ", m^2); if (n==100, return)) ) } \\ _Harry J. Smith_, Oct 18 2009
%Y A065404 Cf. A062700, A000203 (sigma), A065403, A065405, A053182, A053183, A028982.
%K A065404 nonn
%O A065404 1,1
%A A065404 _Labos Elemer_, Nov 06 2001