Lua: Calculate a prime number list

Lua is an extension language.


This script calculates a prime number list starting with smaller ones.


To run this script you need to install lua language: (e.g: in Debian or Ubuntu)
$ sudo aptitude install lua

Current version(when this article was written) is 5.1:
$ sudo aptitude install lua5.1


After installing it, lua interpreter could be found in /usr/bin/lua.

Then you copy this script in a file, e.g: primes.lua and exec:

$ lua primes.lua 20 # it will calculate first twenty prime numbers.

or give execution permissions to the file:
$ chmod a+x primes.lua
$ ./primes.lua 20

#! /usr/bin/lua

local top = tonumber(arg[1])  -- number of primes to calculate

local primes = {2}  -- prime list

local i=3  -- we start with number 3
local total = 1
local sqrt
sqrt = math.sqrt
while(total<top) do
        local is_prime = true
        local max = sqrt(i)  -- we do not need to try with every prime divisor.
        for j=1, total do
                local div = primes[j]
                if(div>max) then
                        break
                end
                if(i%div==0) then
                        is_prime = false  -- currrent number is not prime
                        break
                end
        end
        if(is_prime) then
                table.insert(primes,i)  -- a prime found.
                total = total + 1
        end
        i = i + 2
end

-- show prime number list.
for i=1,# primes do
        print(primes[i])
end

REFERENCE

Lua Tutorial Directory