### More Mods

What is the units digit for the number 123^(456) ?

### N000ughty Thoughts

How many noughts are at the end of these giant numbers?

### Mod 3

Prove that if a^2+b^2 is a multiple of 3 then both a and b are multiples of 3.

# Squaresearch

##### Stage: 4 Challenge Level:

Consider numbers of the form $u_n = 1! + 2! + 3! +...+n!$. How many such numbers are perfect squares?