(a ^ 2) * ((1 - ((1 - a) ^ (2 * k))) / (1 - ((1 - a) ^ 2))) - ((2 * a / k) * ((1 - ((1 - a) ^ k)) / (1 - (1 - a)))) + (1 / k) + (((a ^ 2) * ((1 - a) ^ (2 * k))) / (1 - ((1 - a) ^ 2)))

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