perl -E'$_=pop;sub r{1..$_,reverse 1..$_-1}say" "x(9-$_),r for r' 9
        1
       121
      12321
     1234321
    123454321
   12345654321
  1234567654321
 123456787654321
12345678987654321
 123456787654321
  1234567654321
   12345654321
    123454321
     1234321
      12321
       121
        1