A378278 - OEIS

%I #4 Nov 21 2024 16:05:36

%S 1,0,0,0,1,1,3,7,15,27,51,99,199,403,819,1651,3303,6579,13107,26163,

%T 52327,104755,209715,419635,839271,1678131,3355443,6710067,13420135,

%U 26841907,53687091,107377459,214754919,429503283,858993459,1717973811,3435947623

%N Cogrowth sequence of the 20-element Frobenius group Frob20 = <S,T | S^5, T^4, (ST)^4>.

%F G.f.: (x^6+x^4+x^3-3*x^2+3*x-1) / ((2*x-1) * (x+1) * (x^2+1)/(2*x^2-2*x+1)).

%Y Cf. A078789 (D10), A378254 (C10 X C2), A378276 (Dic20).

%K nonn,easy

%O 0,7

%A _Sean A. Irvine_, Nov 21 2024