code: func (b *base57) numToString(number *big.Int, padToLen int) string {
  	var (
  		out   string
  		digit *big.Int
  	)
  
  	for number.Uint64() > 0 {
  		number, digit = new(big.Int).DivMod(number, big.NewInt(b.alphabet.Length()), new(big.Int))
  		out += b.alphabet.chars[digit.Int64()]
  	}
  
  	if padToLen > 0 {
  		remainder := math.Max(float64(padToLen-len(out)), 0)
  		out = out + strings.Repeat(b.alphabet.chars[0], int(remainder))
  	}
  
  	return out
  }
docs: // numToString converts a number a string using the given alpabet.