a(n) = A026120(2n,n+1).

Terms

a(0) =2a(1) =10a(2) =59a(3) =336a(4) =1922a(5) =11033a(6) =63609a(7) =368197a(8) =2138940a(9) =12464893a(10) =72842371a(11) =426718241a(12) =2505168510a(13) =14735555475a(14) =86824155165a(15) =512368756524