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A182594 Number of prime factors of form cn+1 for numbers 7^n-1 0
1, 1, 2, 1, 2, 2, 1, 3, 3, 2, 2, 1, 4, 2, 3, 2, 4, 2, 3, 1, 4, 3, 4, 3, 3, 4, 4, 3, 3, 3, 2, 4, 3, 3, 3, 3, 4, 4, 5, 3, 4, 2, 4, 2, 4, 2, 3, 4, 4, 5, 5, 3, 5, 1, 6, 3, 4, 4, 5, 4, 6, 2, 3, 6, 6, 4, 6, 3, 8, 2, 5, 5, 5, 3, 2, 3, 7, 2, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,3

LINKS

Table of n, a(n) for n=2..80.

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

EXAMPLE

For n=9, 7^n-1=40353606=2*3^3*19*37*1063 has three prime factors of form, namely 19=2n+1, 37=6n+1, 1063=118n+1. Thus a(9)=3.

MATHEMATICA

m = 7; n = 2; nmax = 80;

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}]

CROSSREFS

Sequence in context: A173306 A276430 A325002 * A201593 A029287 A055184

Adjacent sequences:  A182591 A182592 A182593 * A182595 A182596 A182597

KEYWORD

nonn

AUTHOR

Seppo Mustonen, Nov 22 2010

STATUS

approved

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Last modified January 26 01:48 EST 2020. Contains 331270 sequences. (Running on oeis4.)