a(n) = floor( exp(7/10)*n! ).

Terms

a(0) =2a(1) =4a(2) =12a(3) =48a(4) =241a(5) =1449a(6) =10149a(7) =81194a(8) =730750a(9) =7307505a(10) =80382564a(11) =964590768a(12) =12539679995a(13) =175555519936