What is the value of this sum?
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The sum is equal to n = 2 ∑ ∞ n 2 1 + n 3 1 + n 4 1 . . . = n = 2 ∑ ∞ n 2 1 . n − 1 n = n = 2 ∑ ∞ n . ( n − 1 ) 1 . But ( n − 1 ) . n 1 = n − 1 1 − n 1 and n → ∞ lim n 1 = 0 .So the sum is equal to 2 − 1 1 = 1