Numbers k such that sigma(k-1) - phi(k-1) = (3*k-5)/2.

Terms

a(0) =3a(1) =5a(2) =9a(3) =11a(4) =17a(5) =33a(6) =65a(7) =129a(8) =231a(9) =257a(10) =513a(11) =1025a(12) =2049a(13) =4097a(14) =8193a(15) =16385a(16) =32769a(17) =65537a(18) =119831a(19) =131073a(20) =262145a(21) =524289a(22) =1048577a(23) =2097153a(24) =4194305a(25) =8388609a(26) =16777217a(27) =33554433a(28) =67108865a(29) =134217729