a(n) = A182107(4n+1).

Terms

a(0) =2a(1) =20a(2) =210a(3) =2460a(4) =31122a(5) =410378a(6) =5575682a(7) =77445152a(8) =1093987598a(9) =15660579168a(10) =226608224226