Untitled

let bValues =
   seq { 1..999 }
   |> Seq.filter(fun u -> isPrime (int64 u))

let a,b,len =
   seq { -999..999 }
   |> Seq.filter(fun u ->bValues |> Seq.exists(fun k -> isPrime(int64 (1 + u + k))))
   |> Seq.fold(fun acc a ->
        bValues
        |> Seq.filter(fun k -> isPrime(int64 (1 + a + k)))
        |> Seq.map(fun k -> (a,k))
        |> Seq.append acc
     ) Seq.empty
   |> Seq.map (fun (a,b) ->
        let len =
           Seq.initInfinite(fun n -> (n*n) + (a*n) + b)
           |> Seq.takeWhile(fun k -> isPrime (int64 k))
           |> Seq.length
        (a,b,len)
     )
   |> Seq.maxBy(fun (a,b,len) -> len)

printfn "%d %d -> length: %d;  a*b = %d" a b len (a*b)