Repunits

Algebra Level 3

A repunit is a number that contains only the digit 1, and the repunit of $$n$$ digits is denoted by $$R_{n} = \underbrace{11111 \ldots 1}_{n \text{ times}}$$.

If $$f(x) = 90x^2 + 20x + 1$$, then find the sum of digits of the number $$f(R_{10})$$.

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