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

Author

Felix Fröhlich, Jun 28 2014

Keywords

• nonn
• tabf

Comments

Subsequence of A060443.

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

Examples

			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;
		

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

Crossrefs

Cf. A003260, A016047, A046800, A089162.

Programs

Mathematica

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

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