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

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

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