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

Terms

a(0) =2a(1) =34a(2) =55a(3) =119a(4) =285a(5) =367a(6) =835a(7) =849a(8) =919a(9) =1241a(10) =1505a(11) =1559a(12) =2911a(13) =2914a(14) =2939a(15) =3305a(16) =4149a(17) =4188a(18) =6111a(19) =6903a(20) =7170a(21) =7913a(22) =9360a(23) =10251a(24) =10541a(25) =12566a(26) =15086a(27) =17273a(28) =17759a(29) =17815