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What is the formula for the number sequence 3 7 12 18 25...?
This series is similar to the triangular number sequence 1 3 6 10 15 21.... with the formula n(n+1)/2. So for the number sequence 3 7 12 18 25... I derived a new formula by adding 2n to n(n+1)/2 to get this simplified formula:
[(n*n) + 5n)]/2 (or n squared plus 5n all divided by two)
when n=1, we get [(1*1) + 5(1)]/2=(1+5)/2= 6/2=3
when n=2, we get [(2*2) + 5(2)]/2=(4+10)/2=14/2=7
when n=3, we get [(3*3) + 5(3)]/2=(9+15)/2=24/2=12
when n=4, we get [(4*4) + 5(4)]/2=(16+20)/2=36/2=18
when n=5, we get [(5*5) + 5(5)]/2=(25+25)/2=50/2=25
If we want to know the 10th number in this series, we substitute n by 10 in our formula, we get [(10*10) + 5(10)]/2=(100+50)/2=150/2 = 75
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∙ 11y ago
Anonymous
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