Note that the function accepts extremely big numbers and correctly evaluates them.
For example:
<?php
$v = is_numeric ('58635272821786587286382824657568871098287278276543219876543') ? true : false;
var_dump ($v);
?>
The above script will output:
bool(true)
So this function is not intimidated by super-big numbers. I hope this helps someone.
PS: Also note that if you write is_numeric (45thg), this will generate a parse error (since the parameter is not enclosed between apostrophes or double quotes). Keep this in mind when you use this function.