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 A066514 #14 Aug 09 2023 12:55:08 %S A066514 1,6,55,234,466,758,1704,24587,6656,6718,6428,114210,17158,26180, %T A066514 135869,701426,33277,126920,52320,1341656,469872,87924,48976,50257306, %U A066514 140918,291060,348528,3952920,175438,3685062,285952,12024029,1657948,567994,4624192,15262640,539046,838096 %N A066514 Number of subgroups of the group GL(2,Z_n) of invertible 2 X 2 matrices mod n (sequence A000252). %o A066514 (GAP) c := CyclicGroup(n); aut := AutomorphismGroup(DirectProduct(c,c)); lat := LatticeSubgroups(aut); %o A066514 (Magma) [&+[s`length : s in Subgroups(GL(2,ResidueClassRing(n)))] : n in [2..10]]; // _Robin Visser_, Aug 09 2023 %Y A066514 Cf. A000252. %K A066514 nonn %O A066514 1,2 %A A066514 Sharon Sela (sharonsela(AT)hotmail.com), Jan 04 2002 %E A066514 a(7)-a(11) from _Andrew Howroyd_, Jul 02 2018 %E A066514 More terms from _Robin Visser_, Aug 09 2023