For example, the popular Miller–Rabin primality test can be formulated as a P/poly algorithm: the "advice" is a list of candidate "a" values to test. It is possible to precompute a list of at most "n" values such that every composite "n"-bit number will be certain to have a witness "a" in the list. For example, to correctly determine the primality of 32-bit numbers, it is enough to test "a" = 2, 7, and 61. The existence of short lists of candidate witnesses follows from the fact that for each composite "n", 3/4s of all possible "a" values are witnesses; a simple counting argument similar to the one in the proof that BPP in P/poly below shows that there "exists" a suitable list of "a" values for every input size, although finding it may be expensive.