Question

令a_n為f_n(x)=(1+x)ⁿ⁺¹(n∈N^*)的展開(kāi)式中xⁿ項(xiàng)的系數(shù)，則數(shù)列{a_n}的前n項(xiàng)和為_(kāi)_________________.

Answer 1

 

解析：本題考查二項(xiàng)式定理及數(shù)列求和問(wèn)題.

由題意知a_n=

∴Sn==2+3+4+…+n+n+1

=(1+2+3+…+n)+n=.