Numbers k such that sigma(k) + 4 = sigma(k+4).

Terms

a(0) =3a(1) =7a(2) =13a(3) =19a(4) =37a(5) =43a(6) =67a(7) =79a(8) =97a(9) =103a(10) =109a(11) =127a(12) =163a(13) =193a(14) =223a(15) =229a(16) =277a(17) =307a(18) =313a(19) =349a(20) =379a(21) =397a(22) =439a(23) =457a(24) =463a(25) =487a(26) =499a(27) =613a(28) =643a(29) =673