Summation Formula for Adding by 3's: n(2n+1)/3

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NameIsUnique

I know n(n+1)/2 solves from 1... n by 1's

Is there a formula where you can add up by 3's?

Example: 3 + 6 + 9 + 12 ... n

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Samy_A

NameIsUnique said:

I know n(n+1)/2 solves from 1... n by 1's

Is there a formula where you can add up by 3's?

Example: 3 + 6 + 9 + 12 ... n

Hint: 3+6+9+12=3(1+2+3+4)

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