a(n) = A366470(A366864(n)).

Terms

a(0) =1a(1) =4a(2) =15a(3) =26a(4) =81a(5) =158a(6) =417a(7) =990a(8) =2491a(9) =6402a(10) =17363a(11) =44450a(12) =119773a(13) =326786a(14) =659957a(15) =1845500a(16) =4779649a(17) =9921002a(18) =27575339a(19) =67458614a(20) =187615521a(21) =515594444a(22) =1433794185a(23) =3989181038a(24) =11160791967a(25) =31287537756