a(n) = ((n+1)^2 - 2) * binomial(2*n-2,n-1) / 2.

Terms

a(0) =0a(1) =1a(2) =7a(3) =42a(4) =230a(5) =1190a(6) =5922a(7) =28644a(8) =135564a(9) =630630a(10) =2892890a(11) =13117676a(12) =58903572a(13) =262303132a(14) =1159666900a(15) =5094808200a(16) =22259364120a(17) =96773942790a(18) =418882316490