a(n) = floor(exp(12/17)*n!).

Terms

a(0) =2a(1) =4a(2) =12a(3) =48a(4) =243a(5) =1458a(6) =10209a(7) =81673a(8) =735061a(9) =7350617a(10) =80856796a(11) =970281553a(12) =12613660194a(13) =176591242722