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 A364921 #7 Aug 13 2023 22:40:33 %S A364921 1,4,16,62,48,109,84,2265,324,345,114,5359,217,636,2540,27908,218, %T A364921 2872,272,20933,4089,756,169,780487,892,1813,3015,30562,349,31419,510, %U A364921 191856,5096,1743,14139,115902,685,2156,13191,3764246,662,51063,600,38346,56222,1130,271 %N A364921 Number of conjugacy classes of subgroups of the group GL(2, Z_n) of invertible 2 X 2 matrices mod n. %o A364921 (Magma) [#Subgroups(GL(2, ResidueClassRing(n))) : n in [2..50]]; %o A364921 (Sage) [len(GL(2, Zmod(n)).as_permutation_group().conjugacy_classes_subgroups()) for n in range(2, 50)] %Y A364921 Cf. A000252, A066514. %K A364921 nonn %O A364921 1,2 %A A364921 _Robin Visser_, Aug 12 2023