local suffixes = {
    {1/1000/1000, 'u'},
    {1/1000, 'm'},
    {1, ''},
    {1000, 'K'},
    {1000*1000, 'M'},
    {1000*1000*1000, 'G'},
}

local tests = {
    42,
    0.01,
    1000,
    1024,
    1500,
    1500000,
}

local function formatNumber(num)
    local suffix = { 1, '' }
    for i = 1, #suffixes do
        if num < suffixes[i][1] then
            break
        end
        suffix = suffixes[i]
    end
    return tostring(num / suffix[1]) .. suffix[2]
end

for i = 1, #tests do
    print(formatNumber(tests[i]))
end