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 A066541 #9 Jul 05 2018 02:09:15 %S A066541 1,3,5,12,6,17,8,46,14,22,8,82,12,28,38,112,10,48,12,116,48,28,8,386, %T A066541 18,44,27,140,12,162,16,232,48,38,64,234,18,42,76,596,16,196,16,140, %U A066541 108,28,8,1022,24,66,66,232,12,93,64,680,72,44,8,1032,24,56,204 %N A066541 Number of normal subgroups of the group GL(2,Z_n) of invertible 2 X 2 matrices mod n (sequence A000252). %H A066541 Andrew Howroyd, <a href="/A066541/b066541.txt">Table of n, a(n) for n = 1..100</a> %o A066541 (GAP) Concatenation([1], List([2..20], n->Size(NormalSubgroups(GL(2, Integers mod n))))); # _Andrew Howroyd_, Jul 04 2018 %Y A066541 Cf. A000252, A066514, A316498. %K A066541 nonn %O A066541 1,2 %A A066541 Sharon Sela (sharonsela(AT)hotmail.com), Jan 07 2002 %E A066541 Terms a(16) and beyond from _Andrew Howroyd_, Jul 04 2018