a(n) = binomial(3*n, n + 1)*hypergeom([1, 1 - 2*n], [2 + n], -1).

A321957

a(n) = binomial(3*n, n + 1)*hypergeom([1, 1 - 2*n], [2 + n], -1).

Terms

    a(0) =0a(1) =4a(2) =42a(3) =382a(4) =3302a(5) =27824a(6) =230964a(7) =1898712a(8) =15505590a(9) =126025204a(10) =1020732722a(11) =8245721686a(12) =66477664088a(13) =535118039200

External references