What is the sum of 18 terms of the series starting with 3, 6, 12..
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The first three terms of the series are 3, 6 and 12. Assuming that the other terms of the series share the same property, this is a geometric series with first term 3 and common ratio 2.
The sum of n terms of a geometric series is `(a*(r^n - 1)/(r - 1))`
Here, a = 3 and r = 2
`S_18 = (3*(2^18 - 1)/1) = 786429`
The sum of the first 18 terms of the given series is 786429
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