数列4/3,19/9,82/27,305/81…的前n项和

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数列4/3,19/9,82/27,305/81…的前n项和数列4/3,19/9,82/27,305/81…的前n项和数列4/3,19/9,82/27,305/81…的前n项和有观察可知,此数列的通项公

数列4/3,19/9,82/27,305/81…的前n项和
数列4/3,19/9,82/27,305/81…的前n项和

数列4/3,19/9,82/27,305/81…的前n项和
有观察可知,此数列的通项公式为:An=n+1/3^n
则其前n项和为:
Sn=1+2++……+n+1/3+……+1/3^n
=n(n+1)/2+1/2(1-1/3^n)