an=(a1+a2+...+an)-(a1+a2+...+a(n-1))
=(2^n-1)-[2^(n-1)-1]
=2^n-2^(n-1)
=2^(n-1)
(an)^2=4^(n-1)
(a1)^2+(a2)^2+...+(an)^2=(1-4^n)/(1-4)=(4^n-1)/3
an = 2^n -1
(an)^2
= (2^n -1)^2
=2^(2n) -2^(n+1) + 1
a1^2+a2^2+...+an^2
=(4/3)[ 2^(2n) -1 ] - 4(2^n -1) + (1/2)n(n+1)
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