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

Terms

a(0) =3a(1) =5a(2) =17a(3) =25a(4) =257a(5) =481a(6) =1441a(7) =13825a(8) =65537a(9) =285121a(10) =1425601a(11) =2280961a(12) =2380801a(13) =6690817a(14) =7142401a(15) =11404801a(16) =29719873a(17) =59439745a(18) =100638721a(19) =237758977a(20) =4294967297a(21) =7778073601a(22) =8778792961a(23) =43893964801a(24) =94832640001a(25) =184354652161a(26) =266290053121a(27) =663828480001a(28) =921773260801