The odd part of those numbers which divide the sum of their divisors (A007691).

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =31a(5) =21a(6) =127a(7) =945a(8) =4095a(9) =1023a(10) =544635a(11) =46035a(12) =8191a(13) =355725a(14) =279279a(15) =1796165a(16) =5388495a(17) =180213a(18) =131071a(19) =110800305a(20) =249987465a(21) =42833475a(22) =3112865a(23) =8109585a(24) =524287a(25) =9338595a(26) =49198149a(27) =253255275a(28) =22017975903a(29) =13341660255