A282943 Numbers k such that 3*2^k + 1 is a prime factor of a generalized Fermat number 7^(2^m) + 1 for some m.

8, 12, 36, 276, 408, 2208, 2816, 3168, 3912, 42665, 44685, 59973, 709968, 916773, 1832496

Offset

1,1

Links

Table of n, a(n) for n=1..15.

Anders Björn and Hans Riesel, Factors of generalized Fermat numbers, Math. Comp. 67 (1998), no. 221, pp. 441-446.

Anders Björn and Hans Riesel, Table errata to "Factors of generalized Fermat numbers", Math. Comp. 74 (2005), no. 252, p. 2099.

Anders Björn and Hans Riesel, Table errata 2 to "Factors of generalized Fermat numbers", Math. Comp. 80 (2011), pp. 1865-1866.

OEIS Wiki, Generalized Fermat numbers

Mathematica

lst = {}; Do[p = 3*2^n + 1; If[PrimeQ[p] && IntegerQ@Log[2, MultiplicativeOrder[7, p]], AppendTo[lst, n]], {n, 3912}]; lst

Prog

(Magma) SetDefaultRealField(RealField(400)); IsInteger := func<k | k eq Floor(k)>; [n: n in [2..408] | IsPrime(k) and IsInteger(Log(2, Modorder(7, k))) where k is 3*2^n+1];

Crossrefs

Cf. A078304, A204620, A268657, A268658, A268659, A282944, A268660.

Subsequence of A002253.

Sequence in context: A067681 A132356 A341781 * A024604 A025103 A307652

Adjacent sequences: A282940 A282941 A282942 * A282944 A282945 A282946

Keyword

nonn,hard,more

Author

Arkadiusz Wesolowski, Feb 25 2017

Status

approved