1. Choose a number with repeating 6's and a final 8.
2. The square is made up of:
   • the same number of 4's as there are repeating 6's in the number;
   • one 6
   • the same number of 2's as repeating 6's;
   • a final 4.

   Example:

1. If the number to be squared is 6668:
2. The square has:

   three 4's (same as
   repeating 6's)     4 4 4
one 6                        6
three 2's (same number as
   repeating 3's)              2 2 2
a final 4                            4

3. So the square of 6668 is 44,462,224.

   See the pattern?

1. If the number to be squared is 666668:
2. The square has:

   five 4's (same number as
   repeating 6's)    4 4 4 4 4
one 6                          6
five 2's (same number as
   repeating 6's)                2 2 2 2 2
a final 4                                  4

3. So 666668 × 666668 = 444,446,222,224.