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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 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.)