OFFSET
0,3
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/5)} (-1)^k * binomial(n+k,n) * binomial(2*n-5*k,n).
MATHEMATICA
CoefficientList[InverseSeries[Series[x(1-x)(1+x^5), {x, 0, 28}], x]/x, x] (* Stefano Spezia, Sep 26 2023 *)
PROG
(PARI) a(n) = sum(k=0, n\5, (-1)^k*binomial(n+k, n)*binomial(2*n-5*k, n))/(n+1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Sep 26 2023
STATUS
approved