// BigInteger only has methods to deal with a String or a long value, the latter is used
public BigInteger factorialBigInteger(long n) {
  BigInteger bi = BigInteger.valueOf(2L);
  for (long i = 3L; i <= n; i++) {
    bi = bi.multiply(BigInteger.valueOf(i));
  }
  return bi;
}

floater wrote:
use gamma function

import org.apache.commons.math.special.Gamma;

public class MyGammaTest
{
    public static void main(String[] args)
    {
        double x = 101.0d;
        double y = Math.exp(Gamma.logGamma(x));
        System.out.println(y);
    }
}

floater wrote:
check this java doc. The reason we use 101 is in the reference.
http://jakarta.apache.org/commons/math/apidocs/org/apache/commons/math/special/Gamma.html