Project Euler Problem #2


Sum of even terms in Fibonacci sequence which are < four-million:


 


(1, 1) |> Seq.unfold (fun (a, b) -> Some(a, (b, a + b))) // fibs


|> Seq.takeWhile (fun x -> x <= 4000000)


|> Seq.filter (fun x -> x % 2 = 0)


|> Seq.sum


 


I like how Fibonacci can be represented as a single unfold.

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