A249511 Primes p such that p - 1 and (p + 1)/2 have the same sum of divisors.

3, 5519, 116927, 227663, 263759, 297023, 488639, 616079, 1108127, 2973239, 10738223, 24934079, 25803839, 73277879, 95133239, 117864119, 264054383, 265178591, 285400559, 443052479, 634090679, 644512703, 644615399, 688686959, 717336839

Offset

1,1

Links

Table of n, a(n) for n=1..25.

Example

3 is in this sequence because sigma(3 - 1) = sigma((3 + 1)/2) and 3 is prime.

Mathematica

Select[Prime[Range[10^4]], DivisorSigma[1, # - 1] == DivisorSigma[1, (# + 1)/2] &] (* Alonso del Arte, Oct 31 2014 *)

Prog

(Magma) [p: p in PrimesInInterval(3, 100000000) | SumOfDivisors(p-1) eq SumOfDivisors((p+1) div 2)];
(PARI) lista(nn) = {forprime(p=3, nn, if (sigma(p-1)==sigma((p+1)/2), print1(p, ", ")); ); } \\ Michel Marcus, Oct 31 2014

Crossrefs

Cf. A000203, A171720, A249625.

Sequence in context: A200950 A307210 A171362 * A362099 A248506 A368622

Adjacent sequences: A249508 A249509 A249510 * A249512 A249513 A249514

Keyword

nonn

Author

Juri-Stepan Gerasimov, Oct 31 2014

Status

approved