Online Lemoine’s Conjecture Demo in Go

Lemoine’s conjecture says 2n + 1 = p + 2q always has a solution in primes p and q (not necessarily distinct) for n > 2. This online demo finds p and q for given odd number greater than 5. The demo is written in Go and compiled to JavaScript using GopherJS.

Demo

The following are source code.

HTML

Input Odd Number Greater Than 5: <input type="text" name="n"><br><br>
<button type="button" id="getLemoine">Get Lemoine’s Conjecture</button><br><br>
<textarea id="result" rows="20" cols="50"></textarea>

Go (lemoine.go): This file can be used not only online, but also in your local program. This is the power of GopherJS, which compiles almost all local Go sources without I/O to JavaScript, and makes your code shareable both on frontend and backend.

package main

import (
      "errors"
)

func IsPrime(n int) bool {
      if n < 2 {
              return false
      }

      for i := 2; i*i <= n; i++ {
              if n%i == 0 {
                      return false
              }
      }
      return true
}

func Lemoine(n int) (map[int]int, error) {
      if n <= 5 || n%2 == 0 {
              return nil, errors.New("n must be greater than 5 and must be odd")
      }

      m := make(map[int]int)

      for q := 1; q <= n/2; q++ {
              p := n - 2*q

              if IsPrime(p) && IsPrime(q) {
                      m[p] = q
              }
      }
      return m, nil
}

Go (appdom.go): This file use github.com/siongui/godom. Please go get it before compiling this file.

package main

import (
      . "github.com/siongui/godom"
      "strconv"
)

func main() {
      elmn := Document.QuerySelector("input[name='n']")
      btn := Document.QuerySelector("#getLemoine")
      resultElm := Document.QuerySelector("#result")

      btn.AddEventListener("click", func(e Event) {
              n, err := strconv.Atoi(elmn.Value())
              if err != nil {
                      resultElm.SetValue(err.Error())
                      return
              }
              pqs, err := Lemoine(n)
              if err != nil {
                      resultElm.SetValue(err.Error())
                      return
              }

              text := ""
              for p, q := range pqs {
                      text += elmn.Value() + " = " + strconv.Itoa(p) + " + ( 2 * " + strconv.Itoa(q) + " )\n"
                      resultElm.SetValue(text)
              }
      })
}

The JavaScript equivalent is also available on the demo page [1].

The link of full source code is available on my GitHub repo.

Tested on:

Chromium 65.0.3325.181 on Ubuntu 17.10 (64-bit)
Go 1.10.1
GopherJS 1.10-3

References:

[1]	Online Lemoine’s Conjecture Demo