Smallest k such that 2n - 1 divides sigma(k^2), or 0 if no such k exists.

Terms

a(0) =1a(1) =7a(2) =121a(3) =2a(4) =91a(5) =9a(6) =3a(7) =847a(9) =7a(10) =14a(11) =32a(12) =116281a(13) =1729a(14) =343a(15) =4a(16) =63a(17) =242a(18) =47a(19) =21a(20) =1369a(21) =79a(22) =11011a(23) =2048a(24) =22a(26) =4826809a(27) =961a(28) =7a(29) =4782969a(30) =13a(31) =182