A036827/2.

Terms

a(0) =0a(1) =1a(2) =17a(3) =125a(4) =637a(5) =2637a(6) =9549a(7) =31501a(8) =97037a(9) =283661a(10) =795661a(11) =2158605a(12) =5697549a(13) =14696461a(14) =37175309a(15) =92471309a(16) =226689037a(17) =548667405a(18) =1313079309a(19) =3111125005a(20) =7305429005a(21) =17016291341a(22) =39346765837a(23) =90378862605a(24) =206342979597a(25) =468486979597