a(n) = A306899(n)/6.

Terms

a(0) =1a(1) =2a(2) =6a(3) =8a(4) =15a(5) =30a(6) =49a(7) =96a(8) =189a(9) =360a(10) =693a(11) =1416a(12) =2743a(13) =5516a(14) =10980a(15) =21952a(16) =43707a(17) =87642a(18) =174781a(19) =349920a(20) =699216a(21) =1398804a(22) =2796225a(23) =5594112a(24) =11184875a(25) =22372376a(26) =44739810a(27) =89484080a(28) =178956999a(29) =357926040