A Brier number is a number that is both a Riesel number and a Sierpiński number of the second kind, i.e., a number n such that for all k>=1, the numbers n·2^k + 1 and n·2^k - 1 are composite. The first few are 878503122374924101526292469, 3872639446526560168555701047, 623506356601958507977841221247, ... (OEIS A076335).

Riesel number | Sierpiński number of the second kind