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 A195685 Primes p for which tau(2p-1) = tau(2p+1) = 4. 3
 17, 43, 47, 71, 101, 107, 109, 151, 197, 223, 317, 349, 461, 521, 569, 631, 673, 701, 821, 881, 919, 947, 971, 991, 1051, 1091, 1109, 1153, 1181, 1217, 1231, 1259, 1321, 1361, 1367, 1549, 1693, 1801, 1847, 1933, 1951, 1979, 2143, 2207, 2267, 2297, 2441, 2801 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Sequence terms are a subset of those listed in A086006 and A068497. The numbers 2p-1, 2p, 2p+1 form a run (indeed, a maximal run) of three consecutive integers each with four positive divisors. The first two examples are 33, 34, 35 and 85, 86, 87.  A039833 gives the first number in these maximal 3-integer runs. - Timothy L. Tiffin, Jul 05 2016 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 EXAMPLE tau(2*17-1) = tau(33) = tau(3*11) = 4 = tau(5*7) = tau(35) = tau(2*17+1) and tau(2*43-1) = tau(85) = tau(5*17) = 4 = tau(3*29) = tau(87) = tau(2*43+1). - Timothy L. Tiffin, Jul 05 2016 MAPLE with(numtheory): q:= p-> isprime(p) and tau(2*p-1)=4 and tau(2*p+1)=4: select(q, [\$1..3000])[];  # Alois P. Heinz, Apr 18 2019 MATHEMATICA Select[Prime[Range], DivisorSigma[0, 2 # - 1] == DivisorSigma[0, 2 # + 1] == 4 &] (* T. D. Noe, Sep 22 2011 *) PROG (PARI) lista(nn) = forprime(p=2, nn, if ((numdiv(2*p-1) == 4) && (numdiv(2*p+1) == 4), print1(p, ", "))); \\ Michel Marcus, Jul 06 2016 CROSSREFS Cf. A039833, A068497, A086006. Sequence in context: A196209 A196476 A086006 * A118587 A215164 A123592 Adjacent sequences:  A195682 A195683 A195684 * A195686 A195687 A195688 KEYWORD nonn AUTHOR Timothy L. Tiffin, Sep 22 2011 STATUS approved

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Last modified October 17 11:47 EDT 2019. Contains 328108 sequences. (Running on oeis4.)