Fun with simple math - and a calculator

Not counting the idea of turning the calculator over - I'm just thinking of things that are basic math but is easier to show on a calculator (somewhat).
Squares of sequences of 1's
1 - 1 (obvious)
11 - 121
111 - 12321
1111 - 1234321
11111 - 123454321
111111 - 12345654321
1111111 - 1234567654321
11111111 - 123456787654321
111111111 - 12345678987654321
and if you use hex
1111111111 - 123456789A987654321
So for shits and giggles ask someone what's the square root of 12,345,678,987,654,321 (I won't say it because I can't recall if the English still use the billion = a million million or the American billion = a thousand million but saying it also makes it harder for the victim)?
Squares of sequences of 1's
1 - 1 (obvious)
11 - 121
111 - 12321
1111 - 1234321
11111 - 123454321
111111 - 12345654321
1111111 - 1234567654321
11111111 - 123456787654321
111111111 - 12345678987654321
and if you use hex
1111111111 - 123456789A987654321
So for shits and giggles ask someone what's the square root of 12,345,678,987,654,321 (I won't say it because I can't recall if the English still use the billion = a million million or the American billion = a thousand million but saying it also makes it harder for the victim)?