This code snippet should help you out, as long as number is restricted to numbers.

<?php

// Generate a filtered comma-separated list of the numeric values in numbers.
// Non-numeric values might allow for SQL-injection bugs.
$SQL_numberList = implode(", ", array_filter($numbers, 'is_numeric'));
$sql = mysql_query("SELECT * FROM `number_table` WHERE `number` IN ($SQL_numberList)");

For string arguments in the list you'll need to do something a little different.

No. Use implode() first.