Why does this abreviate not work ? Error down below.

So i made an abbreviation for a rebirth menu, is inside a local script in startergui parent to the textlabel.

local abbreviations = {
    N = 10^30;
    O = 10^27;
    Sp = 10^24;
    Sx = 10^21;
    Qn = 10^18;
    Qd = 10^15;
    T = 10^12;
    B = 10^9;
    M = 10^6;
    K = 10^3
}
local plr = game.Players.LocalPlayer

function abbreviateNums(number)


    local abbreviatedNum = number
    local abbreviationChosen = 0


    for abbreviation, num in pairs(abbreviations) do

        if number >= num and num > abbreviationChosen then

            local shortNum = number / num
            local intNum = math.floor(shortNum)

            abbreviatedNum = tostring(intNum) .. abbreviation .. "+"
            abbreviationChosen = num
        end
    end

    return abbreviatedNum
end




while wait(0.2) do
    script.Parent.Parent.Text = 'You need '.. abbreviateNums(10000 + (1000 * plr.leaderstats.Rebirths.Value)..' Money to rebirth.')
end

ERROR:

Players.ArchangelKingLegacy.PlayerGui.RebirthGui.Frame.TextForTop.TextLabel.LocalScript:24: attempt to compare number <= string  -  Client - LocalScript:24