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A089159 If Mersenne numbers have 3 or more factors, then list the third factor. 1
2089, 2099863, 13264529, 20394401, 212885833, 9361973132609, 1113491139767, 65993, 165799, 1654058017289, 110211473, 70084436712553223, 1489459109360039866456940197095433721664951999121, 7648337, 39940132241, 14732265321145317331353282383 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
A Mersenne number (A001348) is a number of the form 2^p - 1 where p is prime.
EXAMPLE
The 10th Mersenne number 2^29 - 1 = 233*1103*2089 and 2089 is the third prime factor. Notice these factors are congruent to 1 (mod 29).
PROG
(PARI) mersenne2(n) = { c=0; forprime(x=2, n, c++; y = 2^x-1; f=ifactor(y); if(length(f)>=3, print1(f[3]", "); ) ) }
ifactor(n) = { local(f, j, k, flist); flist=[]; f=Vec(factor(n)); for(j=1, length(f[1]), for(k = 1, f[2][j], flist = concat(flist, f[1][j]) ); ); return(flist) }
CROSSREFS
Sequence in context: A106720 A179124 A206606 * A045051 A102504 A270761
KEYWORD
nonn,changed
AUTHOR
Cino Hilliard, Dec 06 2003, corrected Nov 16 2006
EXTENSIONS
a(16) from Amiram Eldar, Jul 11 2024
STATUS
approved

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Last modified July 17 16:16 EDT 2024. Contains 374377 sequences. (Running on oeis4.)