a(n) = T(4,n), array T given by A047858.

Terms

a(0) =1a(1) =6a(2) =17a(3) =41a(4) =93a(5) =205a(6) =445a(7) =957a(8) =2045a(9) =4349a(10) =9213a(11) =19453a(12) =40957a(13) =86013a(14) =180221a(15) =376829a(16) =786429a(17) =1638397a(18) =3407869a(19) =7077885a(20) =14680061a(21) =30408701a(22) =62914557a(23) =130023421a(24) =268435453a(25) =553648125a(26) =1140850685a(27) =2348810237a(28) =4831838205a(29) =9932111869