!! Really Strange !!
http://acm.hust.edu.cn/vjudge/contest/view.action?cid=31329#problem/B
f[ 0 ] = 1 , f[ n ] = f[ n - 1 ] + 2 * （ｎ － １ ），化简得ｆ［ｎ］＝ｎ＾２ － ｎ ＋ ２ ；
import java.math.BigInteger;import java.util.Scanner;public class Main{public static void main(String[] args ){Scanner cin = new Scanner(System.in);while( cin.hasNext()){BigInteger n = cin.nextBigInteger();if( n.equals(BigInteger.valueOf(0))){System.out.println("1");}else{n = n.multiply(n).add(n.negate()).add(BigInteger.valueOf(2));System.out.println(n);}}}}