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

Terms

a(0) =0a(1) =2a(2) =0a(3) =12a(4) =40a(5) =270a(6) =1848a(7) =14840a(8) =133488a(9) =1334970a(10) =14684560a(11) =176214852a(12) =2290793128a(13) =32071103750a(14) =481066556280