a(n) = floor( gamma(n/4) * gamma(n+1)/4 ).

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =27a(5) =159a(6) =1158a(7) =10080a(8) =102786a(9) =1205977a(10) =16050140a(11) =239500800a(12) =3968569039a(13) =72431014665