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%I #4 Nov 11 2024 22:29:21
%S 1,1,2,10,40,136,512,2080,8320,32896,131072,524800,2099200,8390656,
%T 33554432,134225920,536903680,2147516416,8589934592,34359869440,
%U 137439477760,549756338176,2199023255552,8796095119360,35184380477440,140737496743936,562949953421312
%N Cogrowth sequence of the 16-element group C2^2:C4 = <S,T | S^4, T^2, (ST)^2, (S^2T)^2>.
%C Gives the even terms, all the odd terms are 0.
%C Also called K8:C2. Gap identifier 16, 3.
%F G.f.: (12*x^4-14*x^3+8*x^2-5*x+1) / ((4*x-1) * (2*x-1) * (4*x^2+1)).
%Y Cf. A377855 (C4:C4), A054879 (C2^3), A377843 (C4 X C2^2), A377943 (C4 o D4).
%K nonn,easy
%O 0,3
%A _Sean A. Irvine_, Nov 11 2024