let fifth x = x * x * x * x * x

let rec go n sum x =

    if x = 0 then n = sum

    else go n <| sum + fifth (x % 10) <| (x / 10)

let check n = go n 0 n

let mutable sum = 0

for x in 2 .. 10000000 do

    if check x then sum <- sum + x

printfn "%A" sum