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

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SUMMARY

The summation formula for adding numbers by 3's is established as n(2n+1)/3, where n represents the number of terms in the sequence. This formula effectively calculates the sum of the series 3 + 6 + 9 + ... + 3n. The derivation of this formula is based on the observation that the series can be factored to 3 times the sum of the first n natural numbers, which is n(n+1)/2.

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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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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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