A093483(n)-2.

Terms

a(0) =0a(1) =2a(2) =6a(3) =12a(4) =36a(5) =96a(6) =342a(7) =22266a(8) =79806a(9) =187122a(10) =347976a(11) =2171616a(12) =4219797672a(13) =98059918332