Shifts left when Dirichlet convolution (DC:(b,b)->a) applied twice.

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =70a(5) =280a(6) =1168a(7) =4672a(8) =18884a(9) =75632a(10) =303368a(11) =1213472a(12) =4858064a(13) =19432256a(14) =77743040a(15) =310975520a(16) =1243959873a(17) =4975839492a(18) =19903598208a(19) =79614392832a(20) =318458493192