65,537

Number
$65 \,537$ (sixty-five thousand, five hundred and thirty-seven) is:


 * A prime number


 * The $5$th Fermat number and Fermat prime after $3$, $5$, $17$, $257$:
 * $65 \,537 = 2^{\paren {2^4} } + 1 = 2^{16} + 1$

Also see