0

This number is neither prime nor composite.

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, ... .