4

 Properties


 * 4 is the only number whose word form has the same number of letters as the number's cardinality.
 * 2+2, 2*2, and 2^2 all equal 4. The pattern continues through tetration (2^^2) and even array notation (2&m).
 * 4 has more factors than any number less than it making 4 a highly composite number.