OFFSET
1,2
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..1208
FORMULA
a(n) = (n+1)*binomial(3n-2, n-1)/n for n >= 2. [Corrected by Sean A. Irvine, Mar 19 2021]
G.f.: (1+g-7*g^2+3*g^3)/((1-3*g)*(g-1)^2) where g*(1-g)^2 = x. - Mark van Hoeij, Nov 10 2011
D-finite with recurrence 2*n*(2*n-1)*a(n) + (-43*n^2+83*n-34)*a(n-1) + 12*(3*n-5)*(3*n-7)*a(n-2) = 0. - R. J. Mathar, Jul 26 2022
a(n) = (n+1) * A006013(n-1) for n >= 2. - F. Chapoton, Feb 27 2024
MATHEMATICA
MapAt[# - 1 &, Array[(# + 1) Binomial[3 # - 2, # - 1]/# &, 21], 1] (* Michael De Vlieger, Mar 19 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved