204 is a refactorable number.[1] 204 is a square pyramidal number: 204 balls may be stacked in a pyramid whose base is an 8 × 8 square.[2] Its square, 2042 = 41616, is the fourth square triangular number.[3] As a figurate number, 204 is also a nonagonal number[4] and a truncated triangular pyramid number.
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.
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