a(n) = sum(stirling2(n,k)*(k+2)!*(k+3)!, k=1..n)/144.

A262960

a(n) = sum(stirling2(n,k)*(k+2)!*(k+3)!, k=1..n)/144.

Terms

    a(0) =1a(1) =21a(2) =661a(3) =28941a(4) =1678501a(5) =124467021a(6) =11484880261

External references