2925

Number
$2925$ (two thousand, nine hundred and twenty-five) is:


 * $3^2 \times 5^2 \times 13$


 * The $25$th tetrahedral number, after $1$, $4$, $10$, $20$, $35$, $\ldots$, $816$, $969$, $1140$, $1330$, $1540$, $1771$, $2024$, $2300$, $2600$:
 * $2925 = \ds \sum_{k \mathop = 1}^{25} \frac {k \paren {k + 1} } 2 = \dfrac {25 \paren {25 + 1} \paren {25 + 2} } 6$


 * The magic constant of a magic square of order $18$, after $1$, $(5)$, $15$, $34$, $\ldots$, $870$, $1105$, $1379$, $1695$, $2056$, $2465$:
 * $2925 = \ds \dfrac 1 {18} \sum_{k \mathop = 1}^{18^2} k = \dfrac {18 \paren {18^2 + 1} } 2$