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

Terms

a(0) =19a(1) =47a(2) =77a(3) =79a(4) =115a(5) =177a(6) =191a(7) =267a(8) =280a(9) =297a(10) =340a(11) =398a(12) =406a(13) =446a(14) =470a(15) =639a(16) =839a(17) =917a(18) =1240a(19) =1655a(20) =1713a(21) =1778a(22) =1836a(23) =2140a(24) =2157a(25) =4715a(26) =5110a(27) =5269a(28) =6585a(29) =7089