factor 27^140... of course, its only prime factor is 3

factor-num.go

package main

import (
  "fmt"
  "math/big"
  //util "github.com/cznic/mathutil"
)

func Copy(from *big.Int) (*big.Int) { 
  stubby := big.NewInt(1)
  stubby.SetString(from.String(), 10)
  return stubby
}

func main() {
  factors := make(map[uint64]uint64)
  index := big.NewInt(4)
  index.Exp(big.NewInt(27), big.NewInt(140), nil)

  //limit := util.SqrtBig(index)

  div := big.NewInt(1)
  mod := big.NewInt(1)
  zero := big.NewInt(0)
  one := big.NewInt(1)
  for i := big.NewInt(2); i.Cmp(big.NewInt(100)) < 0; {
    div.DivMod(index, i, mod)
    fmt.Println("index: ", index, ", i: ", i)
    fmt.Println("mod: ", mod)

    if mod.Cmp(zero) == 0 {
      factors[i.Uint64()] += 1
      index.SetString(div.String(), 10)
      i = big.NewInt(2)
    } else {
      i.Add(i, one)
    }
  }

  fmt.Println(factors)
}