function isperfect{T<:Integer}(n::T)
    !isprime(n) || return false
    tal = 1//n
    hi = isqrt(n)
    if hi^2 == n
        tal += 1//hi
        hi -= 1
    end
    for i in 2:hi
        (d, r) = divrem(n, i)
        if r == 0
            tal += (1//i + 1//d)
        end
    end
    return tal == 1//1
end

lo = 2
hi = 2^19
println("Searching for perfect numbers from ", lo, " to ", hi, ".")
for i in 2:2^19
    isperfect(i) || continue
    println(@sprintf("%8d", i))
end