（2n+1)(4n²-1)(2n-1)

2^n/n*(n+1) 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 根号【（2n+1）/（n²+n）】平方-4/（n平方+n ）化简 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? 化简：1/(n+1)(n+2)+1/(n+2)(n+3)+1/(n+3)(n+4) (n+1)(n+2)/1 +(n+2)(n+3)/1 +(n+3)(n+4)/1 [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 证明：1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+) 化简(n+1)(n+2)(n+3) n(n+1)(n+2)数列求和 n(n+1)(n+2)等于多少? 若n为正整数,求1/n(n+1)+1/(n+1)(n+2)＋1/(n+2)(n+3)+1/(n+3)(n+4)+.+1/