n(n+1)/1+(n+1)(n+2)/1+.+(n+2007)(n+2008)/1=?

2^n/n*(n+1) (n+1)^n-(n-1)^n=? 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 阶乘(2n-1)!=（2n)!/(2^n*n! Sn=n(n+2)(n+4)的分项等于1/6[n(n+2)(n+4)(n+5)-(n-1)n(n+2)(n+4)]吗? 1 + (n + 1) + n*(n + 1) + n*n + (n + 1) + 1 = 2n^2 + 3n + 3 证明(1+2/n)^n>5-2/n（n属于N+,n>=3) [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 证明n^n-n(n-a)^(n-1)>=n!a.其中n>=a>0 证明:(n+1)n!= (n+1)! 化简(n+1)(n+2)(n+3) n(n+1)(n+2)数列求和