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A371854
a(n) = Sum_{k=0..floor(n/3)} binomial(2*n-k+2,n-3*k).
0
1, 4, 15, 57, 219, 847, 3290, 12819, 50066, 195909, 767790, 3013002, 11837043, 46548919, 183209125, 721628692, 2844297119, 11217639757, 44265835891, 174765349896, 690308413773, 2727823240762, 10783518961394, 42644560775835, 168699835910561, 667580653569309
OFFSET
0,2
FORMULA
a(n) = [x^n] 1/(((1-x)^2-x^3) * (1-x)^(n+1)).
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(2*n-k+2, n-3*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 09 2024
STATUS
approved