get "libhdr"

manifest $(
    MAXIMUM = 20000
$)

// Calculate proper divisors for 1..N
let propDivSums(n) = valof
$(  let v = getvec(n)
    for i = 1 to n do v!i := 1
    for i = 2 to n/2 do
    $(  let j = i*2
        while j < n do
        $(  v!j := v!j + i
            j := j + i
        $)
    $)
    resultis v
$)

// Are A and B an amicable pair, given the list of sums of proper divisors?
let amicable(pdiv, a, b) = a = pdiv!b & b = pdiv!a

let start() be
$(  let pds = propDivSums(MAXIMUM)
    for x = 1 to MAXIMUM do
        for y = x+1 to MAXIMUM do
            if amicable(pds, x, y) do
                writef("%N, %N*N", x, y)
$)