We prove that the number τ = ∑ l = 0 ∞ d l / ∏ j = 1 l ( 1 + d j r + d 2 j s ) , where d ∈ Z , | d | > 1 , and r , s ∈ Q , s ≠ 0 , are such that 1 + d j r + d 2 j s ≠ 0 for any j ∈ Z + , has an irrationality measure 7/3 or 7/2 depending on whether r = − d − h − s d h for some h ∈ N or r 2 ⩽ 4 s . More generally, irrationality measures are given for τ in both the archimedean and p-adic valuations, and also when d , r , s are certain algebraic numbers. For example, we give an effective irrationality measure 7/3 for B d ( d ) , where B q ( z ) is a q-analogue of the Bessel function, and we get effective irrationality measures 7/3 and 7/2 for the p-adic numbers τ p + and τ p − , respectively, where τ p ± = ∑ l = 0 ∞ p l 2 / ∏ j = 1 l ( 1 ± p j ) 2 .
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