a(n) = F(n)-1 mod 2^n+1 with F(n) = n-th Fermat number = 1+2^2^n.

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =1a(5) =4a(6) =16a(7) =4a(8) =1a(9) =256a(10) =16a(11) =4a(12) =4081a(13) =4a(14) =16a(15) =256a(16) =1a(17) =4a(18) =261121a(19) =4a(20) =65536a(21) =256a(22) =16a(23) =4a(24) =65536a(25) =33554305a(26) =16a(27) =67108864a(28) =65536a(29) =4