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 A056643 #5 Mar 30 2012 17:37:41
%S A056643 1,2,5,6,10,25,30,50,65,125,150,190,250,625,750,978,1250,1558,1625,
%T A056643 2405,2425,2575,3125,3750,3890,5050,6250,13250,15150,15625,18750,
%U A056643 25250,31250,40625,71669,72010,75750,78125,93750,95950,96217,99250,115625
%N A056643 Numbers n such that n | 4^n + 3^n + 2^n + 1^n.
%F A056643 All numbers of the forms 5^k, 2*5^k & 6*5^k are in the sequence. - _Farideh Firoozbakht_, Nov 21 2006
%t A056643 Do[ If[ Mod[ PowerMod[ 4, n, n ] + PowerMod[ 3, n, n ] + PowerMod[ 2, n, n ] + 1, n ] == 0, Print[ n ] ], {n, 1, 10^6} ]
%Y A056643 Cf. A001551.
%K A056643 nonn
%O A056643 1,2
%A A056643 _Robert G. Wilson v_, Aug 25 2000