15 = 7 + 8 and 10 = 1 + 2 + 3 + 4. Can you say which numbers can be expressed as the sum of two or more consecutive integers?

Even So

Age 11 to 14 Challenge Level:

Find some triples of whole numbers $ a $, $ b $ and $ c $ such that
$ a^2 + b^2 + c^2 $ is a multiple of 4. Is it necessarily the case
that $ a $, $ b $ and $ c $ must all be even? If so, can you
explain why?