A number can be shown to be a Riesel number by exhibiting a "covering set": a set of prime numbers that will divide any member of the sequence, so called because it is said to "cover" that sequence.
A number can be shown to be a Riesel number by giving its covering set. A covering set is a set of small prime numbers that will divide any member of a sequence, so called because it is said to "cover" that sequence.