A206430 Least k such that k*2^m - 1 has a covering set with precisely n primes.

509203, 777149, 7106977, 60014203

Offset: 6

Author

Arkadiusz Wesolowski, Apr 19 2012

Keywords

• more
• nonn

Comments

A set of primes is a covering set for k*2^m - 1 if for every positive integer m there is some prime in the set which divides k*2^m - 1. Only minimal covering sets are considered here (those which would not remain covering sets with the removal of any element).

Examples

			509203 has the covering set {3, 5, 7, 13, 17, 241}.
777149 has the covering set {3, 5, 7, 13, 19, 37, 73}.
7106977 has the covering set {3, 5, 13, 17, 19, 109, 241, 433}.
60014203 has the covering set {3, 5, 7, 11, 13, 31, 41, 61, 151}.
		

Links

• Wikipedia, Covering set
• Wikipedia, Riesel number

Crossrefs

Cf. A076337, A101036.