Question 62

What is the sum of first 20 terms of the following series?
$$1 \times 2 + 2 \times 3 + 3 \times 4 + 4 \times 5 + ...........$$

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What is the sum of first 20 terms of the following series?$$1 \times 2 + 2 \times 3 + 3 \times 4 + 4 \times 5 + ...........$$