Question

求数列2分之3,4分之9,8分之25,16分之65……的前n项和为?

Answer 1

=(1+1/2)+(2+1/4)+(3+1/8)+…+[n+1/(2^n)]

=(1+2+3+4+…+n)+[1/2+1/(2^2)+1/(2^3)+…+1/(2^n)]

=(1+n)n/2+[1-1/(2^n)]