Log function

Given a how to find the maximum value of n , if 2^n <a
Sol :

public class maxN {
 public static void main(String[] args) {
  System.out.println(log2n(20));
 }
 private static int log2n(int n) {
  return (n > 1) ? 1 + log2n(n / 2) : 0;
 }
}