a(n) = A255473(2^n-1).

Terms

a(0) =1a(1) =6a(2) =24a(3) =88a(4) =336a(5) =1280a(6) =4928a(7) =19072a(8) =74240a(9) =290304a(10) =1139712a(11) =4489216a(12) =17731584a(13) =70197248a(14) =278429696a(15) =1106083840a(16) =4399628288a(17) =17518559232a(18) =69815500800a(19) =278424715264