Nonprimes k such that 9*k divides 2^(k-1) - 1.

Terms

a(0) =1a(1) =1105a(2) =1387a(3) =1729a(4) =2047a(5) =2701a(6) =2821a(7) =3277a(8) =4033a(9) =4369a(10) =4681a(11) =5461a(12) =6601a(13) =7957a(14) =8911a(15) =10261a(16) =10585a(17) =11305a(18) =13741a(19) =13747a(20) =13981a(21) =14491a(22) =15709a(23) =15841a(24) =16705a(25) =18721a(26) =19951a(27) =23377a(28) =29341a(29) =30121