A103665 Primes p such that the number of divisors of p-1 is greater than the number of divisors of p+1.

13, 31, 37, 43, 61, 67, 73, 97, 101, 109, 113, 127, 151, 157, 163, 181, 193, 211, 229, 241, 257, 271, 277, 281, 283, 313, 331, 337, 353, 373, 379, 397, 401, 409, 421, 433, 457, 463, 487, 521, 523, 541, 547, 571, 577, 601, 613, 617, 631, 641, 661, 673, 677

Offset

1,1

Comments

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

Links

Hugo Pfoertner, Table of n, a(n) for n = 1..10000

Example

a(1)=13 because d(12)=6 > d(14)=4.

Mathematica

Select[Prime[Range[2, 140]], Length[Divisors[ # - 1]] > Length[Divisors[ # + 1]] &]
Select[Prime[Range[200]], DivisorSigma[0, #-1]>DivisorSigma[0, #+1]&] (* Harvey P. Dale, Aug 21 2022 *)

Prog

(PARI)
forprime (k=2, 700, if(numdiv(k-1)>numdiv(k+1), print1(k, ", ")))
\\ Hugo Pfoertner, Nov 30 2017

Crossrefs

Cf. A008328 number of divisors of p-1, A008329 number of divisors of p+1, A103664, A103666, A103667.

Sequence in context: A023694 A038465 A391006 * A040050 A040086 A176181

Adjacent sequences: A103662 A103663 A103664 * A103666 A103667 A103668

Keyword

nonn

Author

Hugo Pfoertner, Feb 19 2005

Status

approved