A103664 Primes p such that the number of divisors of p-1 is less than the number of divisors of p+1.

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

Offset: 1

Author

Hugo Pfoertner, Feb 19 2005

Keywords

• nonn

Comments

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

Examples

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

Links

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

Crossrefs

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

Programs

Maple

with(numtheory): p:=proc(n) if isprime(n) and tau(n-1)Emeric Deutsch, Feb 22 2005

Mathematica

Select[Prime[Range[1, 140]], Length[Divisors[ # - 1]] < Length[Divisors[ # + 1]] &]
Select[Prime[Range[200]],DivisorSigma[0,#-1]Harvey P. Dale, May 31 2019 *)