

A089158


Second prime factor, if it exists, of Mersenne numbers.


1



89, 178481, 1103, 616318177, 164511353, 9719, 4513, 69431, 3203431780337, 761838257287, 48544121, 2298041, 202029703, 57912614113275649087721, 13842607235828485645766393, 341117531003194129, 3976656429941438590393
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..17.
Chris Caldwell, MersenneNumbers History.


EXAMPLE

The 5th Mersenne number 2^11  1 = 23*89 and 89 is the second prime divisor.
The 9th Mersenne number 2^23  1 = 47*178481 and 178481 is the second prime divisor.
Notice 23,89 congruent to 1 mod 11 and 47,178481 congruent to 1 mod 23.


PROG

(PARI) mersenne(b, n, d) = { c=0; forprime(x=2, n, c++; y = b^x1; f=factor(y); v=component(f, 1); ln = length(v); if(ln>=d, print1(v[d]", ")); ) }


CROSSREFS

Cf. A016047.
Sequence in context: A128872 A263379 A073905 * A145098 A136031 A145097
Adjacent sequences: A089155 A089156 A089157 * A089159 A089160 A089161


KEYWORD

easy,nonn


AUTHOR

Cino Hilliard, Dec 06 2003


STATUS

approved



