A171720 Primes p such that (p-1)/2 and (p+1)/2 have same sum of divisors.

29, 2729, 29683, 37747, 73133, 149837, 159667, 168269, 185371, 244147, 695477, 880027, 891749, 910747, 1088669, 1298309, 1371991, 1479113, 2414717, 3531329, 6593729, 7452019, 9590311, 13542811, 14527889, 15592877, 18718939, 25650533

Offset

1,1

Comments

If sigma((p-1)/2) is odd then p is of the form n^2+1.

Links

Filip Jevtic, Table of n, a(n) for n=1,..., 78.

Mathematica

Select[Prime[Range[1700000]], DivisorSigma[1, (#-1)/2] == DivisorSigma[1, (#+1)/2]&] (* Harvey P. Dale, Jul 23 2011 *)

Prog

(PARI) for(n=2, 10^6, if(sigma((prime(n)-1)/2)==sigma((prime(n)+1)/2), print(prime(n))))
(Magma) [ p: p in PrimesInInterval(3, 30000000) | SumOfDivisors((p-1) div 2) eq SumOfDivisors((p+1) div 2) ];

Crossrefs

Sequence in context: A370339 A316333 A281440 * A305138 A091751 A144233

Adjacent sequences: A171717 A171718 A171719 * A171721 A171722 A171723

Keyword

nonn

Author

Filip Jevtic (mm07006(AT)alas.math.rs), Dec 16 2009, Dec 19 2009

Status

approved