a(n) = floor(exp(21/23) * n!).

Terms

a(0) =2a(1) =4a(2) =14a(3) =59a(4) =299a(5) =1794a(6) =12559a(7) =100473a(8) =904258a(9) =9042588a(10) =99468475a(11) =1193621707a(12) =15517082198a(13) =217239150785