[root@10-6-8-200 test]# more 1.sh
#!/bin/bash
read -p "please enter a number: " N
for i in $(seq 1 $N)
do
        for x in $(seq 1 $(($N-$i)))
        do
                echo -n " "
        done
        for y in $(seq 1 $(($i*2-1)))
        do
                echo -n "*"
        done
        echo
done
[root@10-6-8-200 test]# ./1.sh
please enter a number: 20
                   *
                  ***
                 *****
                *******
               *********
              ***********
             *************
            ***************
           *****************
          *******************
         *********************
        ***********************
       *************************
      ***************************
     *****************************
    *******************************
   *********************************
  ***********************************
 *************************************
***************************************