OFFSET
1,1
FORMULA
a(n) = A052509(4*n-2,3*n) + A052509(4*n-2,n-1) = 2^(n-2) + Sum_{m=0..n-1} binomial(3*n-1,m) for n >= 2. - Jianing Song, May 30 2022
PROG
(PARI) a(n) = if(n==1, 2, 2^(n-2) + sum(m=0, n-1, binomial(3*n-1, m))) \\ Jianing Song, May 30 2022
CROSSREFS
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
Definition clarified by Eric Rowland, May 29 2022
STATUS
approved