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A182590 Number of prime factors of form cn+1 for numbers 2^n-1 1
1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 2, 1, 1, 2, 3, 2, 1, 2, 2, 1, 2, 3, 3, 1, 2, 1, 2, 2, 3, 2, 2, 3, 2, 2, 4, 3, 3, 2, 3, 3, 3, 1, 4, 4, 3, 3, 2, 3, 2, 3, 5, 2, 2, 1, 2, 3, 4, 2, 3, 2, 3, 1, 4, 3, 3, 3, 4, 5, 3, 1, 5, 3, 2, 3, 4, 2, 3, 2, 4, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,9

LINKS

Seppo Mustonen, Table of n, a(n) for n = 2..200

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

EXAMPLE

For n=10 the prime factors of 2^n-1=1023 are 3,11,31 and 11=n+1, 31=3n+1. Thus a(10)=2.

MATHEMATICA

m = 2; n = 2; nmax = 200;

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: A220163 A102715 A254687 * A047846 A212632 A025885

Adjacent sequences:  A182587 A182588 A182589 * A182591 A182592 A182593

KEYWORD

nonn

AUTHOR

Seppo Mustonen, Nov 22 2010

STATUS

approved

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Last modified March 28 22:27 EDT 2017. Contains 284249 sequences.