1601

Number
$1601$ (one thousand, six hundred and one) is:


 * The $252$nd prime number


 * The $12$th prime number of the form $n^2 + 1$ after $2$, $5$, $17$, $37$, $101$, $197$, $257$, $401$, $577$, $677$, $1297$:
 * $1601 = 40^2 + 1$