a(n) = a(n-1) + 2^a(n-2).A000643a(n) = a(n-1) + 2^a(n-2).Terms a(0) =0a(1) =0a(2) =1a(3) =2a(4) =4a(5) =8a(6) =24a(7) =280a(8) =16777496External referencesoeis: A000643