204 (two hundred [and] four) is the natural number following 203 and preceding 205.
204 is a refactorable number. 204 is a square pyramidal number: 204 balls may be stacked in a pyramid whose base is an 8 ÃÂ 8 square, as it is a sum of all the perfect squares from 1 to 64 (i.e. 1<sup>2</sup> + 2<sup>2</sup> + 3<sup>2</sup> + 4<sup>2</sup> + 5<sup>2</sup> + 6<sup>2</sup> + 7<sup>2</sup> + 8<sup>2</sup> = 204). Its square, 204<sup>2</sup> = 41616, is the fourth square triangular number. As a figurate number, 204 is also a nonagonal number and a truncated triangular pyramid number. 204 is a member of the Mian-Chowla sequence.
There are exactly 204 irreducible quintic polynomials over a four-element field, exactly 204 ways to place three non-attacking chess queens on a 5 ÃÂ 5 board, exactly 204 squares of an infinite chess move that are eight knight's moves from the center, exactly 204 strings of length 11 over a three-letter alphabet with no consecutively-repeated substring, and exactly 204 ways of immersing an oriented circle into the oriented plane so that it has four double points.
Both 204 and its square are sums of a pair of twin primes: 204 = 101 + 103 and 204<sup>2</sup> = 41616 = 20807 + 20809. The only smaller numbers with the same property are 12 and 84.