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A103664 Primes p such that the number of divisors of p-1 is less than the number of divisors of p+1. 7
2, 3, 5, 11, 17, 23, 29, 47, 53, 59, 71, 79, 83, 89, 107, 131, 139, 149, 167, 173, 179, 191, 197, 223, 227, 233, 239, 251, 263, 269, 293, 311, 317, 347, 359, 367, 383, 389, 419, 431, 439, 443, 449, 461, 467, 479, 499, 503, 509, 557, 563, 569, 587, 593, 599, 607 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Mathematica coding by Wouter Meeussen and Robert G. Wilson v.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1)=2 because d(1)=1 < d(3)=2; a(2)=3 because d(2)=2 < d(4)=3.

MAPLE

with(numtheory): p:=proc(n) if isprime(n) and tau(n-1)<tau(n+1) then n else fi end: seq(p(n), n=1..1000); # Emeric Deutsch, Feb 22 2005

MATHEMATICA

Select[Prime[Range[1, 140]], Length[Divisors[ # - 1]] < Length[Divisors[ # + 1]] &]

Select[Prime[Range[200]], DivisorSigma[0, #-1]<DivisorSigma[0, #+1]&] (* Harvey P. Dale, May 31 2019 *)

CROSSREFS

Cf. A008328 number of divisors of p-1, A008329 number of divisors of p+1, A103665, A103666, A103667.

Sequence in context: A040036 A040078 A045309 * A129942 A113239 A049553

Adjacent sequences:  A103661 A103662 A103663 * A103665 A103666 A103667

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Feb 19 2005

STATUS

approved

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Last modified July 11 07:06 EDT 2020. Contains 335609 sequences. (Running on oeis4.)