a(n) = A255283(2^n-1).

Terms

a(0) =1a(1) =7a(2) =31a(3) =145a(4) =601a(5) =2551a(6) =10351a(7) =42433a(8) =170761a(9) =690247a(10) =2768191a(11) =11123185a(12) =44543161a(13) =178525591a(14) =714455311a(15) =2860291873a(16) =11443638121a(17) =45791846887a(18) =183184681951a(19) =732859788625