A249625 Primes p such that (p-1)/2 and p+1 have the same sum of divisors.

24001, 95881, 205633, 2266177, 3792673, 3850393, 6846241, 7448641, 15498121, 21566497, 25267681, 28987681, 48114841, 57207697, 69805261, 79176001, 90257521, 110360641, 121223761, 129642001, 139752001, 164655793, 166175461, 185983981, 211268881, 264159601

Offset

1,1

Links

Table of n, a(n) for n=1..26.

Example

24001 is in this sequence because A000203((24001-1)/2) = A000203(24001+1) = 39312 and 24001 is prime.

Mathematica

Select[Prime[Range[1442*10^4]], DivisorSigma[1, (#-1)/2]==DivisorSigma[ 1, #+1]&] (* Harvey P. Dale, Dec 13 2018 *)

Prog

(Magma)  [p: p in PrimesInInterval(3, 100000000) | SumOfDivisors((p-1) div 2) eq SumOfDivisors(p+1)];
(PARI) forprime(p=3, 10^8, if(sigma((p-1)\2)==sigma(p+1), print1(p, ", "))) \\ Colin Barker, Nov 02 2014

Crossrefs

Cf. A000203, A171720, A249511.

Sequence in context: A263156 A263153 A233882 * A263036 A259733 A295451

Adjacent sequences: A249622 A249623 A249624 * A249626 A249627 A249628

Keyword

nonn

Author

Juri-Stepan Gerasimov, Nov 02 2014

Status

approved