2*A002740(n).

Terms

a(0) =0a(1) =0a(2) =0a(3) =4a(4) =30a(5) =168a(6) =840a(7) =3960a(8) =18018a(9) =80080a(10) =350064a(11) =1511640a(12) =6466460a(13) =27457584a(14) =115892400a(15) =486748080a(16) =2035917450a(17) =8485840800a(18) =35263382880a(19) =146157442200a(20) =604404010980