a(n) = (1/2)*A291036(n).

Terms

a(0) =1a(1) =3a(2) =8a(3) =23a(4) =66a(5) =188a(6) =537a(7) =1533a(8) =4376a(9) =12493a(10) =35664a(11) =101812a(12) =290649a(13) =829731a(14) =2368680a(15) =6762003a(16) =19303866a(17) =55107824a(18) =157319377a(19) =449108397a(20) =1282094784a(21) =3660067465a(22) =10448598672a(23) =29828197224a(24) =85152217777a(25) =243088784019a(26) =693959105912