a(n) = Sum_{k=0..n} S(k)*S(n-k), convolution of S=A001644 with itself.

Terms

a(0) =9a(1) =6a(2) =19a(3) =48a(4) =89a(5) =190a(6) =391a(7) =784a(8) =1577a(9) =3142a(10) =6219a(11) =12256a(12) =24041a(13) =46974a(14) =91471a(15) =177568a(16) =343753a(17) =663814a(18) =1278979a(19) =2459152a(20) =4719417a(21) =9041470a(22) =17294039a(23) =33030320a(24) =62999145a(25) =120006214a(26) =228327099a(27) =433939904a(28) =823854793a(29) =1562602238