1 ^ 2 + 1 = 1 * 2 2 ^ + 2 = 2 * 3 3 ^ 2 + 3 = 3 * 4

1 ^ 2 + 1 = 1 * 2 2 ^ + 2 = 2 * 3 3 ^ 2 + 3 = 3 * 4

n^2+n=n*(n+1)
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