1+3+5+7+9......（2n-1）+（2n+1）+（2n+3）＝(1+2n+3)(n+2)/2＝(n+2)(n+2)＝(n+2)^2
1+3+5+7+9......（2n-1）+（2n+1）+（2n+3）=(1+2n+3)×（n+2）÷2=（n+2）²
（n+2）的平方
