Shell Script to print first n natural numbers in a pattern of Equilateral Triangle

Program

read -p "Enter Number: " number
for((row=1;row<=number;row++))
do
	for((spaces=row;spaces<=number;spaces++))
	do
		echo -ne " "
	done
	for((j=1;j<=row;j++))
	do
		echo -ne "$j"
	done
	for((l=(row-1);l>=1;l--))
	do
		echo -ne "$l"
	done
	echo
done

Output

$ chmod 755 number_pattern_2.sh
$ sh number_pattern_2.sh
Enter Number: 4
    1
   121
  12321
 1234321