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A249625 Primes p such that (p-1)/2 and p+1 have the same sum of divisors. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 19 17:48 EDT 2019. Contains 323395 sequences. (Running on oeis4.)