go run prime.go NumberOfDigits

prime.go

package main

import (
	"fmt"
	"os"
	"strconv"
)

func main() {
	// RSA-2048 is a decimal number of 617 digits
	numDigits, err := strconv.Atoi(os.Args[1])
	if err != nil {
		panic(err)
	}
	m := makeMatrix(digitNumberToInt(numDigits))
	purge(m, 0)
}

func digitNumberToInt(digits int) int {
	res := ""
	for i := 0; i < digits; i++ {
		fmt.Println("Composing number:", i)
		res = res + "9"
	}
	fmt.Println("Converting string to number", res)
	r, err := strconv.Atoi(res)
	if err != nil {
		panic(err)
	}
	fmt.Println("Done")
	return r
}

func purge(m []int, n int) {
	if n%1000 == 0 {
		fmt.Println("Purge iteration:", n, "/", len(m))
	}
	if len(m) == n {
		for _, n := range m {
			if n != 0 {
				fmt.Print(strconv.Itoa(n) + " ")
			}
		}
		fmt.Println()
		os.Exit(0)
	}
	if m[n] < 2 || m[n] == 0 {
		purge(m, n+1)
	}
	for i := 0; i < len(m); i++ {
		if m[i] != 0 && m[i] != m[n] && m[i]%m[n] == 0 {
			m[i] = 0
		}
	}
	purge(m, n+1)
}

func makeMatrix(num int) []int {
	matrix := []int{}
	for i := 2; i < num; i++ {
		if i%1000 == 0 {
			fmt.Println("Initializing matrix:", i, "/", num)
		}
		if i%2 != 0 {
			matrix = append(matrix, i)
		}
	}
	return matrix
}