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A244453 Prime factors of 2^A054723(n)-1, ordered by increasing n, then by increasing size of the factors. 1
23, 89, 47, 178481, 233, 1103, 2089, 223, 616318177, 13367, 164511353, 431, 9719, 2099863, 2351, 4513, 13264529, 6361, 69431, 20394401, 179951, 3203431780337, 193707721, 761838257287, 228479, 48544121, 212885833 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A060443.

Prime factors of composite Mersenne numbers; A089162 with the Mersenne primes A000668 removed. - Jens Kruse Andersen, Jul 11 2014

LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 1..577

Sergey Nikitin, Euler-Fermat algorithm and some of its applications, 2018.

Sam Wagstaff, The Cunningham Project

EXAMPLE

A054723(1) = 11. 2^11-1 = 2047 = 23*89. - Jens Kruse Andersen, Jul 11 2014

Triangle begins:

23, 89;

47, 178481;

233, 1103, 2089;

223, 616318177;

13367, 164511353;

431, 9719, 2099863;

2351, 4513, 13264529;

6361, 69431, 20394401;

MATHEMATICA

Map[FactorInteger, Select[2^Prime@Range@20 - 1, CompositeQ]][[All, All, 1]] // Flatten (* Michael De Vlieger, Nov 20 2018 *)

PROG

(PARI) forprime(n=1, 100, m=2^n-1; if(!isprime(m), f=factor(m); for(i=1, #f~, print1(f[i, 1]", ")))) \\ Jens Kruse Andersen, Jul 11 2014

CROSSREFS

Cf. A003260, A016047, A046800, A089162.

Sequence in context: A044591 A050255 A014088 * A158537 A117049 A142062

Adjacent sequences:  A244450 A244451 A244452 * A244454 A244455 A244456

KEYWORD

nonn,tabf

AUTHOR

Felix Fröhlich, Jun 28 2014

STATUS

approved

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Last modified May 24 00:38 EDT 2019. Contains 323528 sequences. (Running on oeis4.)