%I #11 Aug 15 2025 05:39:06

%S 2,2,6,22,58,146,414,1206,3410,9634,27670,79926,230666,667058,1936174,

%T 5632662,16408866,47875650,139908774,409404630,1199368026,3517351890,

%U 10325547582,30339113718,89217594738,262561101282,773248631222,2278737199606

%N Co-growth function of a certain group.

%H Stephen P Humphries, <a href="https://doi.org/10.1017/S030500419600134X">Cogrowth of groups and the Dedekind-Frobenius group determinant</a>, Mathematical Proceeding of the Cambridge Philosophical Society volume 121 Part 2 pages 193-217 (1997).

%F G.f. (x+1) * sqrt(1-x) / sqrt((1-3*x) * (3*x^2+1)) [from Humphries]. - _Sean A. Irvine_, Feb 26 2018

%F D-finite with recurrence n*a(n) +(-3*n+1)*a(n-1) +2*(n+1)*a(n-2) -6*n*a(n-3) +3*(-n+6)*a(n-4) +9*(n-5)*a(n-5)=0. - _R. J. Mathar_, Aug 15 2025

%K nonn

%O 1,1

%A _Stephen P. Humphries_

%E More terms from _Sean A. Irvine_, Feb 26 2018