a(n) = floor(exp(1/24)*n!).

Terms

a(0) =1a(1) =2a(2) =6a(3) =25a(4) =125a(5) =750a(6) =5254a(7) =42035a(8) =378319a(9) =3783194a(10) =41615136a(11) =499381635a(12) =6491961263a(13) =90887457690