a(n) = A354655(n)/3, for n >= 1.

Terms

a(0) =1a(1) =9a(2) =49a(3) =210a(4) =765a(5) =2492a(6) =7434a(7) =20700a(8) =54420a(9) =136360a(10) =327789a(11) =760102a(12) =1707342a(13) =3728025a(14) =7935525a(15) =16507152a(16) =33624045a(17) =67186077a(18) =131891825a(19) =254710260a(20) =484474753a(21) =908538081a(22) =1681364124a(23) =3073166600a(24) =5551851375a(25) =9919925145a(26) =17541289017a(27) =30714092066a(28) =53279031420