open System
    let rec s (d:DateTime) = seq {
            yield d
            yield! s (d.AddDays(1.0))
        }
    let sd = DateTime.Parse("2015/01/01")
    let ed = DateTime.Parse("2015/12/31")
    s sd
    |> Seq.takeWhile ((>=)ed)
    |> Seq.filter (fun d ->
        let dd = d.ToString("dd") |> Seq.map (string >> int) |> Seq.reduce((+))
        int(d.ToString("MM")) = dd
    ) |> Seq.length
    |> printfn "%A"