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 A221951 #7 Sep 30 2018 10:42:24
%S A221951 3,8,6,15,6,16,6,22,9,16,6,30,6,16,12,29,6,24,6,30,12,16,6,44,9,16,12,
%T A221951 30,6,32,6,36,12,16,12,45,6,16,12,44,6,32,6,30,18,16,6,58,9,24,12,30,
%U A221951 6,32,12,44,12,16,6,60,6,16,18,43,12,32,6,30,12,32,6,66,6,16,18,30,12,32,6,58
%N A221951 Number of subgroups of C_4 X C_n.
%H A221951 Antti Karttunen, <a href="/A221951/b221951.txt">Table of n, a(n) for n = 1..65537</a>
%F A221951 a(n) = Sum_{d|n} (1+gcd(2,d)+gcd(4,d)). - _Antti Karttunen_, Sep 30 2018
%o A221951 (PARI) A221951(n) = sumdiv(n,d,(1+gcd(2,d)+gcd(4,d))); \\ _Antti Karttunen_, Sep 30 2018
%Y A221951 Row 4 of A216624.
%Y A221951 Cf. A000005, A069735.
%K A221951 nonn
%O A221951 1,1
%A A221951 _N. J. A. Sloane_, Feb 02 2013