let answer = Seq.init_infinite (fun x -> Int32.to_string (9*(x+1))) |> Seq.find (String.for_all (fun digit -> (int_of_char digit) % 2 = 0))

However, the initial solution is much easier to understand than these new ones.

I don’t know if there is a better way, I’ll test a little bit more and let you know.

Thanks for the suggestion!


head$filter (all (`elem` "02468") . show) [9,18..]


If that’s visible at all, that’s the way I’d do it in Haskell. I don’t know the F# syntax or libs so well, but you might be able to simplify your solution along these lines. Using show to break things into digits is a bit of a hack, but show is the only use case for digitization significant enough for inclusion in the standard libs – I can’t quite convince myself it’s wrong, since digits are fundamentally defined fundamentally as a display concern.