login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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
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 * A360053 A129942 A113239
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Feb 19 2005
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 29 16:00 EST 2024. Contains 370425 sequences. (Running on oeis4.)