Erdős Problem #249 - Discussion thread

Is\[\sum_n \frac{\phi(n)}{2^n}\]irrational? Here $\phi$ is the Euler totient function.

number theory | irrationality

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The decimal expansion of this sum is A256936 on the OEIS.

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This page was last edited 28 September 2025.

External data from the database - you can help update this
Formalised statement? Yes
Related OEIS sequences: A256936

When referring to this problem, please use the original sources of Erdős. If you wish to acknowledge this website, the recommended citation format is:

T. F. Bloom, Erdős Problem #249, https://www.erdosproblems.com/249, accessed 2025-11-16

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