

A182591


Number of prime factors of form cn+1 for numbers 3^n1


1



0, 1, 1, 2, 2, 1, 1, 1, 3, 2, 2, 1, 2, 1, 2, 2, 3, 2, 2, 2, 4, 2, 2, 2, 2, 4, 3, 3, 4, 3, 2, 1, 5, 2, 4, 2, 4, 4, 2, 3, 5, 2, 3, 3, 3, 4, 5, 5, 4, 2, 4, 3, 6, 3, 2, 5, 6, 2, 3, 2, 5, 2, 2, 4, 5, 3, 3, 2, 3, 1, 4, 4, 5, 3, 5, 4, 9, 3, 3, 3, 5, 4, 5, 4, 3, 4
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OFFSET

2,4


LINKS

Seppo Mustonen, Table of n, a(n) for n = 2..170
S. Mustonen, On prime factors of numbers m^n+1
Seppo Mustonen, On prime factors of numbers m^n+1 [Local copy]


EXAMPLE

For n=6, 3^n1=728 has two prime factors of the form cn+1, namely 7=n+1 and 13=2n+1. Thus a(6)=2.


MATHEMATICA

m = 3; n = 2; nmax = 170;
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: A066855 A175685 A331182 * A321393 A058914 A238585
Adjacent sequences: A182588 A182589 A182590 * A182592 A182593 A182594


KEYWORD

nonn


AUTHOR

Seppo Mustonen, Nov 22 2010


STATUS

approved



