OFFSET
1,1
LINKS
Stephen P Humphries, Cogrowth of groups and the Dedekind-Frobenius group determinant, Mathematical Proceeding of the Cambridge Philosophical Society volume 121 Part 2 pages 193-217 (1997).
FORMULA
G.f. (x+1) * sqrt(1-x) / sqrt((1-3*x) * (3*x^2+1)) [from Humphries]. - Sean A. Irvine, Feb 26 2018
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
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Feb 26 2018
STATUS
approved