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%I #7 Sep 30 2018 10:42:24
%S 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 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 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 Number of subgroups of C_4 X C_n.
%H Antti Karttunen, <a href="/A221951/b221951.txt">Table of n, a(n) for n = 1..65537</a>
%F a(n) = Sum_{d|n} (1+gcd(2,d)+gcd(4,d)). - _Antti Karttunen_, Sep 30 2018
%o (PARI) A221951(n) = sumdiv(n,d,(1+gcd(2,d)+gcd(4,d))); \\ _Antti Karttunen_, Sep 30 2018
%Y Row 4 of A216624.
%Y Cf. A000005, A069735.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Feb 02 2013