225

Number
$225$ (two hundred and twenty-five) is:


 * $2^2 \times 3^2$


 * The $15$th square number after $1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196$:
 * $225 = 15^2$


 * The $9$th octagonal number, after $1, 8, 21, 40, 65, 96, 133, 176$:
 * $225 = 1 + 7 + 13 + 19 + 25 + 31 + 37 + 43 + 49 = 9 \left({3 \times 9 - 2}\right)$


 * The sum of the first $5$ cubes:
 * $225 = 1^3 + 2^3 + 3^3 + 4^3 + 5^3$