a(n) = floor(exp(22/23) * n!).

Terms

a(0) =2a(1) =5a(2) =15a(3) =62a(4) =312a(5) =1873a(6) =13117a(7) =104937a(8) =944441a(9) =9444416a(10) =103888585a(11) =1246663020a(12) =16206619263a(13) =226892669691