Primes p such that p - 1 and (p + 1)/2 have the same sum of divisors.

Terms

a(0) =3a(1) =5519a(2) =116927a(3) =227663a(4) =263759a(5) =297023a(6) =488639a(7) =616079a(8) =1108127a(9) =2973239a(10) =10738223a(11) =24934079a(12) =25803839a(13) =73277879a(14) =95133239a(15) =117864119a(16) =264054383a(17) =265178591a(18) =285400559a(19) =443052479a(20) =634090679a(21) =644512703a(22) =644615399a(23) =688686959a(24) =717336839