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A244453 Prime factors of 2^A054723(n)-1, ordered by increasing n, then by increasing size of the factors. 1

%I

%S 23,89,47,178481,233,1103,2089,223,616318177,13367,164511353,431,9719,

%T 2099863,2351,4513,13264529,6361,69431,20394401,179951,3203431780337,

%U 193707721,761838257287,228479,48544121,212885833

%N Prime factors of 2^A054723(n)-1, ordered by increasing n, then by increasing size of the factors.

%C Subsequence of A060443.

%C Prime factors of composite Mersenne numbers; A089162 with the Mersenne primes A000668 removed. - _Jens Kruse Andersen_, Jul 11 2014

%H Jens Kruse Andersen, <a href="/A244453/b244453.txt">Table of n, a(n) for n = 1..577</a>

%H Sergey Nikitin, <a href="https://www.researchgate.net/profile/S_Nikitin2/publication/326632583_Euler-Fermat_algorithm_and_some_of_its_applications/links/5b74458592851ca6506380fc/Euler-Fermat-algorithm-and-some-of-its-applications.pdf">Euler-Fermat algorithm and some of its applications</a>, 2018.

%H Sam Wagstaff, <a href="http://homes.cerias.purdue.edu/~ssw/cun/">The Cunningham Project</a>

%e A054723(1) = 11. 2^11-1 = 2047 = 23*89. - _Jens Kruse Andersen_, Jul 11 2014

%e Triangle begins:

%e 23, 89;

%e 47, 178481;

%e 233, 1103, 2089;

%e 223, 616318177;

%e 13367, 164511353;

%e 431, 9719, 2099863;

%e 2351, 4513, 13264529;

%e 6361, 69431, 20394401;

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

%o (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

%Y Cf. A003260, A016047, A046800, A089162.

%K nonn,tabf

%O 1,1

%A _Felix Fröhlich_, Jun 28 2014

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Last modified August 6 15:06 EDT 2020. Contains 336248 sequences. (Running on oeis4.)