<?php function dv($r){$s=1;for($m=0;$r!=0;$r/=10)$s=($s+$r%10*(9-$m++%6))%11; return chr($s?$s+47:75);} ?>
$rut = 1; $dv = dv($rut); // 9 $rut = 99; $dv = dv($rut); // k