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 A260507 #17 Aug 20 2015 13:18:00 %S A260507 2,7,179,619,17807 %N A260507 Primes p such that (2^p+1)^(p-1) == 1 (mod p^2). %C A260507 A000040(n) such that A260531(n) = 1. %C A260507 Is this a subsequence of A130060? %C A260507 a(6) > 10325801 if it exists. %C A260507 a(6) > 3037000499 if it exists. - _Hiroaki Yamanouchi_, Aug 20 2015 %e A260507 2^7 + 1 = 129 and 129^6 == 1 (mod 7^2), so 7 is a term of the sequence. %t A260507 Select[Prime@ Range@ 120, Mod[(2^# + 1)^(# - 1), #^2] == 1 &] (* _Michael De Vlieger_, Jul 29 2015 *) %o A260507 (PARI) forprime(p=2, , if(Mod(2^p+1, p^2)^(p-1)==1, print1(p, ", "))) %Y A260507 Cf. A098640, A127074, A130060, A130062, A260531. %K A260507 nonn,hard,more %O A260507 1,1 %A A260507 _Felix Fröhlich_, Jul 27 2015