a(n)=sum(i+j+k=n,(2n)!/(i+j)!/(j+k)!/(k+i)!) 0<=i<=n, 0<=j<=n, 0<=k<=n.

A092472

a(n)=sum(i+j+k=n,(2n)!/(i+j)!/(j+k)!/(k+i)!) 0<=i<=n, 0<=j<=n, 0<=k<=n.

Terms

    a(0) =1a(1) =6a(2) =54a(3) =510a(4) =4830a(5) =45486a(6) =425502a(7) =3956238a(8) =36594558a(9) =337038702a(10) =3093092574a(11) =28302208974a(12) =258331692606

External references