a(n) = (n!)^3 * Sum_{k=0..n} k^2/(k!)^3.

A368771

a(n) = (n!)^3 * Sum_{k=0..n} k^2/(k!)^3.

Terms

    a(0) =0a(1) =1a(2) =12a(3) =333a(4) =21328a(5) =2666025a(6) =575861436a(7) =197520472597

External references