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Task/Amicable-pairs/Futhark/amicable-pairs.futhark

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+fun divisors(n: int): []int =
+  filter (fn x => n%x == 0) (map (1+) (iota (n/2)))
+
+fun amicable((n: int, nd: int), (m: int, md: int)): bool =
+  n < m && nd == m && md == n
+
+fun getPair (divs: [upper](int, int)) (flat_i: int): ((int,int), (int,int)) =
+  let i = flat_i / upper
+  let j = flat_i % upper
+  in unsafe (divs[i], divs[j])
+
+fun main(upper: int): [][2]int =
+  let range = map (1+) (iota upper)
+  let divs = zip range (map (fn n => reduce (+) 0 (divisors n)) range)
+  let amicable = filter amicable (map (getPair divs) (iota (upper*upper)))
+  in map (fn (np,mp) => [np.0, mp.0]) amicable