Duplicate of A002653.

Terms

a(0) =1a(1) =6a(2) =24a(3) =56a(4) =114a(5) =168a(6) =280a(7) =294a(8) =444a(9) =390a(10) =840a(11) =636a(12) =1176a(13) =1176a(14) =1512