Largest Prime factor of 1e12 number

gistfile1.go

// Works for 13195 and larger numbers like 901234567 but fails when I add a digit let alone for 600851475143.

// The prime factors of 13195 are 5, 7, 13 and 29
// What is the largest prime factor of the number 600851475143

package main

import (
  "fmt"
)

func main() {
  var (
    i int64
    target int64
  )

  i = 2
  target = 901234567 // 600851475143 // 13195
  primes := make([]int64, 0)

  for i < target {
    if isFactor(target, i) {
      if isPrime(i) {
        primes = append(primes, i)
      }
    }
    i += 1
  }

  fmt.Printf("%d\n", primes)

  largest := primes[len(primes)-1]
  fmt.Printf("%d\n", largest)
}

func isFactor(target int64, possible_factor int64) (bool) {
  if target % possible_factor == 0 {
    return true
  } else {
    return false
  }
}

func isPrime(target int64) (bool) {
  if target == 1 {
    return false
  }
  prime := true
  var i int64
  i = 2
  for i < target {
    if isFactor(target, i) {
      prime = false
      break
    }
    i += 1
  }
  return prime
}