a(n) = hypergeom([1/2 - n/2, -n/2], [-n], -56).

Terms

a(0) =1a(1) =1a(2) =15a(3) =29a(4) =239a(5) =645a(6) =3991a(7) =13021a(8) =68895a(9) =251189a(10) =1215719a(11) =4732365a(12) =21752431a(13) =88005541a(14) =392539575a(15) =1624617149a(16) =7120171199a(17) =29864811285a(18) =129547208071a(19) =547654566061