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 A238983 #23 Oct 02 2014 12:06:05
%S A238983 1,2,265,49217,7870171,592258417
%N A238983 Numbers n such that the sum of n-th powers of unitary divisors of n is congruent to -1 modulo n.
%C A238983 a(7) > 10^10. - _Hiroaki Yamanouchi_, Oct 02 2014
%t A238983 AA[n_, k_] := AA[n, k] = Mod[Sum[If[GCD[i, n] == i && GCD[i, n/i] == 1, PowerMod[i, k, n], 0], {i, n}], n]; Select[Range[1000], Mod[AA[#, #], #] == #-1 &]
%o A238983 (PARI) isok(n) = (sumdiv(n, d, d^n*(gcd(d, n/d) == 1)) % n) == (n-1); \\ _Michel Marcus_, Sep 30 2014
%o A238983 (PARI) isok(n) = sumdiv(n, d, if (gcd(d, n/d) == 1, Mod(d, n)^n)) == Mod(n-1, n); \\ _Michel Marcus_, Oct 02 2014
%Y A238983 Cf. A034448, A238981, A238982.
%K A238983 nonn,more,hard
%O A238983 1,2
%A A238983 _José María Grau Ribas_, Mar 07 2014
%E A238983 a(4)-a(5) from _Hiroaki Yamanouchi_, Sep 30 2014
%E A238983 a(6) from _Hiroaki Yamanouchi_, Oct 02 2014