Problem #30: A Story of 1's and 2's
Write, side by side, the numeral 1 an even number of times.
Subtract from the number thus formed the number obtained by writing,
side by side, a series of 2s half the length of the first number. You will
always get a perfect square. For instance,
1111 - 22 = 1089 = 332
Can you say why this is?