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Number Theory Level 3

$\large f(x) = 1 + x + x^2 + x^3 + x^4 + x^5$

What is the smallest positive integer $x$ such that the decimal representation of $f(x)$ does not contain the digit 6?

1 solution

Giorgos K.
Feb 22, 2018

just checked the first 10 values on Mathematica

Table[Sum[x^n, {n, 0, 5}], {x, 10}]

{6, 63, 364, 1365, 3906, 9331 , 19608, 37449, 66430, 111111}