ConwaySequence or Look-and-say sequence. http://en.wikipedia.org/wiki/Look-and-say_sequence

ConwaySequence.java

/**
 * Conway Sequence
 *
 * @see http://en.wikipedia.org/wiki/Look-and-say_sequence
 * @author Thiago Prates
 */
public class ConwaySequence {

    /**
     * Generate a element at position n according to *Conway Sequence*.
     *
     * @param long n Position in the sequence.
     * @return long Element at position supplied by user.
     */
    public static String get(long n) {
        if (n < 0) {
            throw new IllegalArgumentException();
        }

        StringBuilder s = new StringBuilder("1");
        StringBuilder ret = new StringBuilder();
        char currentNumber;
        long num;

        while (n > 0) {
            for (int i = 0, len = s.length(); i < len;) {
                currentNumber = s.charAt(i);

                num = 1;
                for (int j = i + 1; j < len && currentNumber == s.charAt(j); j++) {
                    num++;
                }
                
                ret.append(num).append(currentNumber);

                i += num;
            }

            s = ret;
            ret = new StringBuilder();
            n--;
        }

        return s.toString();
    }

    public static void main(String[] args) {
        System.out.println(ConwaySequence.get(Long.parseLong(args[0])));
    }
}