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 A260531 #13 Aug 10 2015 16:35:19
%S A260531 1,0,21,1,45,79,120,305,484,697,404,186,1354,603,612,2757,945,3051,
%T A260531 3552,498,950,1186,2657,1781,6403,9192,8035,1927,2181,2713,6097,2621,
%U A260531 10139,3476,10878,8608,22609,21028,24550,19031,1,12852,33426,27793,34279,11543
%N A260531 a(n) = (2^p+1)^(p-1) modulo p^2, where p is prime(n).
%C A260531 The primes where a(n) == 1 are given by A260507.
%H A260531 Felix Fröhlich, <a href="/A260531/b260531.txt">Table of n, a(n) for n = 1..10000</a>
%F A260531 a(n) = A098640(n)^(A000040(n)-1) modulo A000040(n)^2.
%t A260531 f[n_] := Block[{p = Prime@ n}, PowerMod[2^p + 1, p - 1, p^2]]; Array[f, 46] (* _Robert G. Wilson v_, Jul 29 2015 *)
%o A260531 (PARI) a(n) = lift(Mod(2^prime(n)+1, prime(n)^2)^(prime(n)-1))
%Y A260531 Cf. A000040, A098640, A260507.
%K A260531 nonn
%O A260531 1,3
%A A260531 _Felix Fröhlich_, Jul 28 2015