(2n)^2-1=(2n+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 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 求教,N^0+N^1+N^2+N^3.N^n=?公式是什么?(N≠n且N,n都属于自然数） 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? 求证：C(0,n)+2C(1,n)+.+(n+1)C(n,n)=2^n+2^(n-1)