Erdős Problem 69 #
Reference: erdosproblems.com/69
theorem
Erdos69.erdos_69 :
Irrational (∑' (n : ℕ), ↑(ArithmeticFunction.cardDistinctFactors (n + 2)) / 2 ^ (n + 2))
Is $$ \sum_{n\geq 2}\frac{\omega(n)}{2^n} $$ irrational? (Here $\omega(n)$ counts the number of distinct prime divisors of $n$.)
Tao observed that erdos_69
is a special case of erdos_257
, since
$$ \sum_{n\geq 2}\frac{\omega(n)}{2^n} = \sum_p \frac{1}{2^p - 1}. $$