425

Number
$425$ (four hundred and twenty-five) is:


 * $5^2 \times 17$


 * The $17$th pentagonal number after $1$, $5$, $12$, $22$, $35$, $51$, $70$, $92$, $117$, $145$, $176$, $210$, $247$, $287$, $330$, $376$:
 * $425 = \displaystyle \sum_{k \mathop = 1}^{17} \paren {3 k - 2} = \dfrac {17 \paren {3 \times 17 - 1} } 2$


 * The $33$rd generalized pentagonal number after $1$, $2$, $5$, $7$, $12$, $15$, $\ldots$, $222$, $247$, $260$, $287$, $301$, $330$, $345$, $376$, $392$:
 * $425 = \displaystyle \sum_{k \mathop = 1}^{17} \paren {3 k - 2} = \dfrac {17 \paren {3 \times 17 - 1} } 2$