a(n) = floor( Gamma(n + 1/4)/Gamma(1/4) ).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =2a(5) =9a(6) =50a(7) =318a(8) =2310a(9) =19060a(10) =176310a(11) =1807181a(12) =20330788a(13) =249052161a(14) =3299941145a(15) =47024161317a(16) =717118460090