a(n) = hypergeom([1/2 - n/2, -n/2], [-n], -8*n).

Terms

a(0) =1a(1) =1a(2) =5a(3) =13a(4) =89a(5) =341a(6) =2653a(7) =13021a(8) =110449a(9) =648469a(10) =5891381a(11) =39734685a(12) =382729801a(13) =2887493077a(14) =29287115341a(15) =242592910621