Scratch

print(" /\\  /\\ ath")
print("/  \\/  \\ adness")
print("How high should the numbers be? (not the answer): ")
n = io.read("*n")

if (n == nil) then
    print("No number found. Choosing 10.")
    n = 10
end

function prob()
    math.randomseed(tonumber(tostring(os.time()):reverse():sub(1,6))) -- Better random numbers
    print("\n")
    x = math.random(4)
    if (x == 1) then
        x = "+"
    elseif (x == 2) then
        x = "-"
    elseif (x == 3) then
        x = "*"
    elseif (x == 4) then
        x = "/"
    end
    x = tostring(math.random(n) .. x .. math.random(n))
    print(x)
    y = io.read("*n")
    x = loadstring(x)()
    if (y == x) then
        print(y .. " is correct.")
    else
        print(y .. " is incorrect.")
    end
    prob()
end

prob()

...\Desktop\Hunter - Other\Lua stuff\test.lua:27: attempt to call a nil value
stack traceback:
        ...\Desktop\Hunter - Other\Lua stuff\test.lua:27: in function 'prob'
        ...\Desktop\Hunter - Other\Lua stuff\test.lua:36: in main chunk
        [C]: in function 'dofile'
        stdin:1: in main chunk
        [C]: ?

dofile("C:\\Users\\Owner\\Desktop\\Hunter - Other\\Lua stuff\\test.lua")