Is the sum of the first n items of sequence 1 - A ^ 2 - A ^ 3? Sequence 1 - A ^ 2 - A ^ 3 What is the sum of the first n items? | Math enthusiast | Mathematical art

Is the sum of the first n items of sequence 1 - A ^ 2 - A ^ 3? Sequence 1 - A ^ 2 - A ^ 3 What is the sum of the first n items?

When a = 1, an = n, then Sn = (1 + n) * n / 2;
When a! = 1, an = (1-A ^ n) / (1-A), then Sn = [1-A + 1-A ^ 2 +... 1-A ^ n] / (1-A) = [n - (a + A ^ 2 +... A ^ n)] / (1-A) = [n-a * (1-A ^ n) / (1-A)] / (1-A)

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