a(n) = A142710(n)/2.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =19a(5) =56a(6) =138a(7) =407a(8) =999a(9) =2851a(10) =7113a(11) =19702a(12) =49954a(13) =135461a(14) =347553a(15) =929567a(16) =2403759a(17) =6374236a(18) =16564458a(19) =43697227a(20) =113896339a(21) =299525051a(22) =782121453a(23) =2053027082a(24) =5366641794a(25) =14071792681a(26) =36807232413a(27) =96449857207a(28) =252375716899a(29) =661078086176