a(n) = 6^n/n! * Product_{k=0..n-1} (6*k - 1).

A004996

a(n) = 6^n/n! * Product_{k=0..n-1} (6*k - 1).

Terms

    a(0) =1a(1) =-6a(2) =-90a(3) =-1980a(4) =-50490a(5) =-1393524a(6) =-40412196a(7) =-1212365880a(8) =-37280250810

External references