Numbers k such that phi(k) divides (sigma(k+1) + sigma(k-1)).

Terms

a(0) =2a(1) =3a(2) =4a(3) =6a(4) =32a(5) =34a(6) =54a(7) =55a(8) =58a(9) =70a(10) =84a(11) =133a(12) =141a(13) =221a(14) =285a(15) =322a(16) =377a(17) =407a(18) =472a(19) =664a(20) =684a(21) =988a(22) =1149a(23) =1241a(24) =1505a(25) =1911a(26) =1978a(27) =2230a(28) =2590a(29) =2631