a(n) = gcd(2*n, 4^n)^(2*n + 1) mod (2^(2*n + 1) - 1)^2.

Terms

a(0) =0a(1) =8a(2) =63a(3) =128a(4) =1534a(5) =2048a(6) =16383a(7) =32768a(8) =524285a(9) =524288a(10) =4194303a(11) =8388608a(12) =100663294a(13) =134217728a(14) =1073741823a(15) =2147483648a(16) =42949672956a(17) =34359738368a(18) =274877906943a(19) =549755813888