There are exactly 204 irreduciblequinticpolynomials over a four-element field, exactly 204 ways to place three non-attacking chess queens on a 5 × 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 2042 = 41616 = 20807 + 20809. The only smaller numbers with the same property are 12 and 84.
In other fields
In telecommunications, area code 204 is a North American telephone area code for the Canadian province of Manitoba. 204 is one of the original 86 area codes assigned in 1947 in the contiguous United States and the then-nine-province extent of Canada. More recently a second area code (431) was added to allow for the expanding phone number distribution within the province.
204 is the HTTP status code indicating the request was successfully fulfilled and that there is no additional content to send in the response payload body.