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 A124924 #9 Aug 23 2013 21:21:50
%S A124924 5,13,173,5501
%N A124924 Primes p such that p^2 divides A124923((3p-1)/2) = ((3p-1)/2)^(3(p-1)/2) + 1.
%C A124924 p divides A124923((3p-1)/2) for primes p in A003628. Hence this sequence is a subsequence of A003628.
%C A124924 Also, primes p such that (-2)^((p-1)/2) == -1-3p/2 (mod p^2).
%C A124924 No other terms below 10^11.
%e A124924 5 is in this sequence because A124923((3*5-1)/2) = A124923(7) = 7^8 + 1 = 117650 is divisible by 5^2 = 25.
%t A124924 Do[ p = Prime[n]; m = (3p-1)/2; f = PowerMod[ m, m-1, p^2 ] + 1; If[ IntegerQ[ f/p^2 ], Print[p] ], {n,2,10000} ]
%Y A124924 Cf. A124923, A003628.
%K A124924 hard,more,nonn
%O A124924 1,1
%A A124924 _Alexander Adamchuk_, Nov 12 2006
%E A124924 Edited by _Max Alekseyev_, Jan 28 2012