Carl1: @p=(1);for(2..10000){if(!$n[$_]){push@p,$_;for($k=$_*$_;$k<=10000;$n[$k]=1,$k+=$_){}}} Carl2: @p=(1,2);for($_=3;$_<=10000;$_+=2){if(!$n[$_]){push@p,$_;for($k=$_*$_;$k<=10000;$n[$k]=1,$k+=$_){}}}