a(n) = (n+1)!! mod n!!.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =7a(5) =3a(6) =9a(7) =69a(8) =177a(9) =60a(10) =2715a(11) =4500a(12) =42975a(13) =104580a(14) =91665a(15) =186795a(16) =3493665a(17) =13497435a(18) =97345395a(19) =442245825a(20) =2601636975a(21) =13003053525a(22) =70985324025a(23) =64585694250a(24) =57891366225