a(n) = n*(a(n-1) + 1), a(0) = 0.

Terms

a(0) =0a(1) =1a(2) =4a(3) =15a(4) =64a(5) =325a(6) =1956a(7) =13699a(8) =109600a(9) =986409a(10) =9864100a(11) =108505111a(12) =1302061344a(13) =16926797485a(14) =236975164804