xponential notation is returned.
    </p>
    <p>
      If <code>base</code> is <code>null</code> or undefined it is ignored.
      <br />
      See <a href='#Errors'>Errors</a> for the treatment of other non-integer or
      out of range <code>base</code> values.
    </p>
    <pre>
x = new BigNumber(750000)
x.toString()                    // '750000'
BigNumber.config({ EXPONENTIAL_AT : 5 })
x.toString()                    // '7.5e+5'

y = new BigNumber(362.875)
y.toString(2)                   // '101101010