The Beauty of Number 9 in building a pyramid of 1's

The Beauty of Number 9 in building a pyramid of 1's

0 x 9 + 1   = 1
01 x 9 + 2   = 11
012 x 9 + 3   = 111
0123 x 9 + 4   = 1111
01234 x 9 + 5   = 11111
012345 x 9 + 6   = 111111
0123456 x 9 + 7   = 1111111
01234567 x 9 + 8   = 11111111
012345678 x 9 + 9   = 111111111
0123456789 x 9 + 10 = 1111111111