TriangularNumbers.fsx

////Helper functions////
let getTrianglesAndCoPrimes n = 
    if n % 2 = 0 then (n*(n+1)/2, (n/2), (n+1))
    else (n*(n+1)/2,((n+1)/2), n) 

let getDivisors n = 
    let rec loopAndCheck n i divisors =
        if i > n/2 then divisors |> Set.ofArray
        elif n % i = 0 then loopAndCheck n (i+1) (Array.append divisors [|i|])
        else loopAndCheck n (i+1) divisors 
    
    loopAndCheck n 1 [||]

let checkCoPrime n1 n2 = 
    not (getDivisors n1 
        |> Set.intersect (getDivisors n2)
        |> Set.exists (fun x -> x <> 1))


////Actual calculation////
[|1..100000|]
|> Array.map getTrianglesAndCoPrimes
|> Array.map (fun (x, y, z) -> checkCoPrime y z)
|> Array.filter (fun x -> x = false) // should be an empty array