OFFSET
0,1
FORMULA
a(n) = A052509(4*n,3*n+1) + A052509(4*n,n) = 2^(n-1) + Sum_{m=0..n} binomial(3*n,m). for n >= 1. - Jianing Song, May 30 2022
PROG
(PARI) a(n) = if(n==0, 2, 2^(n-1) + sum(m=0, n, binomial(3*n, m))) \\ Jianing Song, May 30 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved