a(n) = A047848(4, n).

Terms

a(0) =1a(1) =2a(2) =9a(3) =58a(4) =401a(5) =2802a(6) =19609a(7) =137258a(8) =960801a(9) =6725602a(10) =47079209a(11) =329554458a(12) =2306881201a(13) =16148168402a(14) =113037178809a(15) =791260251658