# Non-Abundant Sums drill

function ProperDivisors(n::Int64)
    q = min(1000, n)
    z = Array{Int64}(undef, q)
    z[1] = 1
    c = 1

    for d = 2:round(Int64, sqrt(n))
        w, r = divrem(n, d)

        if r == 0
            c += 1
            z[c] = d
            c += 1
            z[c] = w
        end
    end

    return sort(z[1:c])
end

function IsAbundant(n::Int64)
    z = ProperDivisors(n)
    return (sum(z) > n)
end

function CanBeWrittenAsSumOfAN(n::Int64)
    if n > 28123; return true; end
    n2 = div(n, 2)

    for x = 12:n2
        if IsAbundant(x)
            y = n - x
            if IsAbundant(y); return true, (x, y); end
        end
    end

    return false
end

function main(N::Int64 = 28123)
    for n = 1:26
        if !CanBeWrittenAsSumOfAN(n)[1]; print(n, " "); end
    end

    for n = 27:2:N # no point checking for even numbers any more
        if !CanBeWrittenAsSumOfAN(n)[1]; print(n, " "); end
    end
end