Is it true that every real number x satisfying x=∑_n∈Nfracsigma(n)2^n is irrational, where sigma(n) is the sum-of-divisors function?

Erdős Problem #250 — Irrationality of a Divisor-Sum Series

Is it true that every real number $x$ satisfying

x=\sum_{n\in\mathbb{N}}\frac{\sigma(n)}{2^n}

is irrational, where $\sigma(n)$ is the sum-of-divisors function?

References

Posted 1 month ago · edited 3 weeks ago

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