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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 (list; graph; refs; listen; history; text; internal format)
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^x-1; 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

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Last modified January 19 12:48 EST 2020. Contains 331049 sequences. (Running on oeis4.)