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A137258 Primes p that satisfy s-t < 0 where s = sigma(2*p+1) mod phi(p) and t = sigma(2*p+1) mod p. 0
3, 5, 7, 17, 19, 139, 157, 577, 1201, 27361, 530401, 2513281, 7183201, 407817217 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The function sigma(n) is the sum of positive divisors function and the function phi(n) is the Euler totient function.

The positive values of s-t for primes p<2000 are 0, 2, 3, 4.

a(15) > 2*10^9. - Donovan Johnson, Feb 15 2013

LINKS

Table of n, a(n) for n=1..14.

PROG

(PARI) p=1; for(i=1, 10^9, p=nextprime(p+1); s=sigma(2*p+1); if(s%(p-1)<s%p, print(p))) /* Donovan Johnson, Feb 15 2013 */

CROSSREFS

Sequence in context: A125739 A219461 A122853 * A053341 A331894 A086086

Adjacent sequences:  A137255 A137256 A137257 * A137259 A137260 A137261

KEYWORD

nonn,more

AUTHOR

Juan Lopez Gonzalez (juan.lopezg(AT)estudiante.uam.es), Apr 25 2008

EXTENSIONS

a(10)-a(12) added by R. J. Mathar, May 23 2008

a(13)-a(14) from Donovan Johnson, Feb 15 2013

STATUS

approved

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Last modified August 14 19:09 EDT 2020. Contains 336483 sequences. (Running on oeis4.)