login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Smallest nonempty set S containing prime divisors of 7k + 1 for each k in S.
0

%I #11 Jul 09 2018 21:25:37

%S 2,3,5,11,13,23

%N Smallest nonempty set S containing prime divisors of 7k + 1 for each k in S.

%e 7 * 2 + 1 = 15 = 3 * 5, both of which are in the set.

%e 7 * 3 + 1 = 22 = 2 * 11, both of which are in the set.

%e 7 * 5 + 1 = 36 = 2^2 * 3^2; both 2 and 3 are in the set.

%e 7 * 11 + 1 = 78 = 2 * 3 * 11, all three of which are in the set.

%e 7 * 13 + 1 = 92 = 2^2 * 23; both 2 and 23 are in the set.

%e 7 * 23 + 1 = 162 = 2 * 3^4; both 2 and 3 are in the set.

%Y Cf. A020575, A020581, A020587, A020602.

%K nonn,fini,full

%O 1,1

%A _David W. Wilson_