a(n) = n!/(k!)^2, where k is the largest number such that (k!)^2 divides n!.

Terms

a(0) =1a(1) =2a(2) =6a(3) =6a(4) =30a(5) =20a(6) =140a(7) =70a(8) =630a(9) =7a(10) =77a(11) =924a(12) =12012a(13) =3432a(14) =51480a(15) =12870a(16) =218790a(17) =48620a(18) =923780a(19) =184756a(20) =3879876a(21) =705432a(22) =16224936a(23) =2704156a(24) =67603900a(25) =10400600a(26) =280816200a(27) =178296a(28) =5170584a(29) =155117520