The percentage of positive integers that are prime is 0%. That is, if π(n) is the number of primes less than n, then as n gets larger and larger, π(n)/n gets closer and closer to 0 (the limit is 0). [Caldwell]
In any ring, for every prime there is another prime which can be added to it to get 0. Discussion of the natural primes, by contrast, does not require knowledge of 0's existence. [Merickel]
Zero is the smallest of the k-digit numbers whose digit(s) are the number of distinct prime factors in each of the following k integers. The sequence begins 0, 1, 12, 21, 22422, 24223, 33333, 34441524, 4242436235, 23443535352, 34462443242, 35256523324, 4341535435353, 4645441523344, 5244526446515, 5335524234335, ... .