$serialnumber = 2120718412451 พอแยกตัวเลขออกมาแล้วเราจะเอามาเพื่อมาทำการคำนวณ

for ( $i = 0; $i < strlen($serialnumber); $i++ ) 
			{
				$lend = $serialnumber[$i];
				if($lend == 0){
					$num = 0;
				}
				if($lend == 1){
					$num = (49-48);
				}
				if($lend == 2){
					$num = (50-48);
				}
				if($lend == 3){
					$num = (51-48);
				}
				if($lend == 4){
					$num = (52-48);
				}
				if($lend == 5){
					$num = (53-48);
				}
				if($lend == 6){
					$num = (54-48);
				}
				if($lend == 7){
					 $num = (55-48);
				}
				if($lend == 8){
					$num = (56-48);
				}
				if($lend == 9){
					$num = (57-48);
				}
					
			}//end for