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A182595 Number of prime factors of form cn+1 for numbers 2^n+1 1
1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 2, 1, 2, 2, 3, 1, 1, 2, 2, 1, 2, 2, 3, 2, 2, 2, 3, 2, 1, 2, 2, 1, 2, 1, 4, 2, 2, 1, 3, 3, 2, 2, 3, 2, 2, 3, 2, 3, 3, 1, 4, 2, 2, 4, 4, 2, 2, 2, 2, 2, 2, 2, 4, 2, 3, 3, 5, 1, 2, 3, 4, 5, 3, 2, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,13

COMMENTS

Repeated prime factors are counted.

LINKS

Seppo Mustonen, Table of n, a(n) for n = 2..250

S. Mustonen, On prime factors of numbers m^n+-1

EXAMPLE

For n=14, 2^n+1=16385=5*29*113 has two prime factors of form, namely 29=2n+1, 113=8n+1. Thus a(14)=2.

MATHEMATICA

m = 2; n = 2; nmax = 250;

While[n <= nmax, {l = FactorInteger[m^n + 1]; s = 0;

     For[i = 1, i <= Length[l],

      i++, {p = l[[i, 1]];

       If[IntegerQ[(p - 1)/n] == True, s = s + l[[i, 2]]]; }];

     a[n] = s; } n++; ];

Table[a[n], {n, 2, nmax}]

Table[{p, e}=Transpose[FactorInteger[2^n+1]]; Sum[If[Mod[p[[i]], n] == 1, e[[i]], 0], {i, Length[p]}], {n, 2, 50}]

CROSSREFS

Sequence in context: A328966 A077479 A070106 * A109706 A174541 A029444

Adjacent sequences:  A182592 A182593 A182594 * A182596 A182597 A182598

KEYWORD

nonn

AUTHOR

Seppo Mustonen, Nov 24 2010

STATUS

approved

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Last modified January 28 06:29 EST 2020. Contains 331317 sequences. (Running on oeis4.)