a(n) = (n-1)*(a(n-1)+a(n-2)+a(n-3)).

Terms

a(0) =0a(1) =1a(2) =1a(3) =6a(4) =32a(5) =195a(6) =1398a(7) =11375a(8) =103744a(9) =1048653a(10) =11637720a(11) =140691287a(12) =1840531920a(13) =25907192051a(14) =390437813612