procedure main(arglist)
limit := \arglist[1] | 100000
write("Perfect numbers from 1 to ",limit,":")
every write(isperfect(1 to limit))
write("Done.")
end

procedure isperfect(n)         #: returns n if n is perfect
local sum,i

every (sum := 0) +:= (n ~= divisors(n))
if sum = n then return n
end

link factors