let d n =
let mutable sum = 0
for i in 1 .. n / 2 do
if n % i = 0 then
sum <- sum + i
sum
[ 1 .. 10000 ]
|> Seq.fold (fun sum n ->
let x = d n
if x > n && d x = n then sum + n + x
else sum
) 0
|> printfn "%A"
