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nth term can be calculated from the formula (n - 1) x n/2.

Eg 8th term = 7 x 4 ie 28; 42nd term = 41 x 21 ie 861.

If the series starts at 1 rather than 0, the formula is (n + 1) x n/2

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A:

(n2-n) ÷ 2

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12y ago

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