a(n) = A055086(n!).

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =20a(5) =52a(6) =140a(7) =400a(8) =1203a(9) =3808a(10) =12634a(11) =43771a(12) =157821a(13) =590518a(14) =2287070a(15) =9148286a(16) =37719353a(17) =160029667a(18) =697553152a(19) =3119552536a(20) =14295585635a(21) =67052240163a(22) =321571247089