497

Number
$497$ (four hundred and ninety-seven) is:


 * $7 \times 71$


 * The $1$st counterexample to Greenwood's Conjecture:
 * $497 = T_{31} + 1 = \dfrac {31 \times \paren {31 + 1} } 2 + 1$ but is not prime


 * The $2$nd number such that the result when adding $2$ is the reversal of when multiplying by $2$:
 * $497 + 2 = 499$; $497 \times 2 = 994$


 * The $26$th number whose $\sigma$ value is square:

Also see

 * Greenwood's Conjecture