euler12

euler12.fsx

let factors number = seq {
    for divisor in 1 .. (float >> sqrt >> int) number do
    if number % divisor = 0 then
        yield divisor
        if number <> 1 then yield number / divisor //special case condition: when number=1 then divisor=(number/divisor), so don't repeat it
}

let rec triangle n = match n with
                        | 0 -> 0
                        | 1 -> 1
                        | n -> n + triangle(n-1)
    
let r = {1..100000} |> Seq.map(triangle) |> Seq.skipWhile(fun tri -> Seq.length(factors(tri)) <= 500) |> Seq.take(1)

printfn "%A" (Seq.toList r)