a(n) = A306896(n)/6.

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =5a(5) =14a(6) =21a(7) =48a(8) =87a(9) =180a(10) =341a(11) =704a(12) =1365a(13) =2758a(14) =5475a(15) =10976a(16) =21845a(17) =43806a(18) =87381a(19) =174960a(20) =349573a(21) =699402a(22) =1398101a(23) =2797008a(24) =5592425a(25) =11186188a(26) =22369797a(27) =44742040a(28) =89478485a(29) =178962840