Least k such that 2^n = k^2-sigma(k)*phi(k).

Terms

a(0) =2a(1) =4a(2) =8a(3) =16a(4) =32a(5) =12a(6) =20a(7) =256a(8) =44a(9) =1024a(10) =2048a(11) =4096a(12) =8192a(13) =16384a(14) =992a(15) =65536a(16) =724a(17) =262144a(18) =2080a(19) =1048576a(20) =16256a(21) =4194304a(22) =8388608a(23) =16777216a(24) =33554432a(25) =67108864a(26) =48832a(27) =268435456a(28) =536870912a(29) =1073741824