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Large repunit factors

Problem 132

Published on Friday, 1st December 2006, 06:00 pm; Solved by 3162

A number consisting entirely of ones is called a repunit. We shall define R(k) to be a repunit of length k.

For example, R(10) = 1111111111 = 11×41×271×9091, and the sum of these prime factors is 9414.

Find the sum of the first forty prime factors of R(109).