Calculation of 'e'

function sigma(start, finish, callback)
    local sum = 0
    for n = start, finish do
        sum = sum + callback(n)
    end
    return sum
end

function factorial(n)
    local product = 1
    for i = 1, n do
        product = product * i
    end
    return product
end

local e = sigma(0, 5000, function(n)
    return 1 / factorial(n)
end)

print(e)