The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 3 17:54 EDT 2022. Contains 355055 sequences. (Running on oeis4.)