Convolution of A008549 with A000302 (powers of 4).

Terms

a(0) =0a(1) =1a(2) =10a(3) =69a(4) =406a(5) =2186a(6) =11124a(7) =54445a(8) =259006a(9) =1205790a(10) =5519020a(11) =24918306a(12) =111250140a(13) =492051124a(14) =2159081192a(15) =9409526397a(16) =40766269774a(17) =175707380630a(18) =753876367356