A000522(n+2)-A000522(n).

Terms

a(0) =4a(1) =14a(2) =60a(3) =310a(4) =1892a(5) =13374a(6) =107644a(7) =972710a(8) =9754500a(9) =107518702a(10) =1292197244a(11) =16818292374a(12) =235673103460