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A341660 Primes p such that p^2 - 1 has fewer than 32 divisors. 0
2, 3, 5, 7, 11, 13, 17, 19, 23, 31, 37, 47, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For all primes p > 73, p^2 - 1 has at least A309906(2)=32 divisors.

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

      p =            factorization

   n  a(n)  p^2 - 1    of p^2 - 1    tau(p^2 - 1)

  --  ----  -------  --------------  ------------

   1    2        3   3                     2

   2    3        8   2^3                   4

   3    5       24   2^3 * 3               8

   4    7       48   2^4 * 3              10

   5   11      120   2^3 * 3 * 5          16

   6   13      168   2^3 * 3 * 7          16

   7   17      288   2^5 * 3^2            18

   8   19      360   2^3 * 3^2 * 5        24

   9   23      528   2^4 * 3 * 11         20

  10   31      960   2^6 * 3 * 5          28

  11   37     1368   2^3 * 3^2 * 19       24

  12   47     2208   2^5 * 3 * 23         24

  13   73     5328   2^4 * 3^2 * 37       30

MATHEMATICA

Select[Range[100], PrimeQ[#] && DivisorSigma[0, #^2 - 1] < 32 &] (* Amiram Eldar, Feb 26 2021 *)

CROSSREFS

Cf. A000005, A000040, A309906, A341655, A341658.

Sequence in context: A334797 A229060 A219528 * A046501 A033875 A105581

Adjacent sequences:  A341657 A341658 A341659 * A341661 A341662 A341663

KEYWORD

nonn,fini,full

AUTHOR

Jon E. Schoenfield, Feb 26 2021

STATUS

approved

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Last modified May 9 10:11 EDT 2021. Contains 343728 sequences. (Running on oeis4.)