CollapseProblem 68Is ∑n≥21n!−1\sum_{n\geq 2}\frac{1}{n!-1}n≥2∑n!−11 irrational?Source: erdosproblems.com/68Number theoryIrrationalityWiki pageStatusOpenNo claim settles this problem.ReferencesEr88cErdős, P., On the irrationality of certain series: problems and results. New advances in transcendence theory (Durham, 1986) (1988), 102-109.