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My 10yo son said he noticed something odd about multiplication.
If you have some number C, then (C+1)*(C-1) is 1 less than C*C.
We started exploring and it worked with any C we tried.
We tried +/-2 and it was 4 less. He said he thought it was going by the square.
So we tried +/-3 and yep, it was 9 less.
C doesn't have to be an integer either.
It was a cool pattern he noticed and it was fun getting to explore math with him.
He surprised me a bit with that kind of an insight.