Question 396669
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Hi

{{{a[n] = 2*(-2)^(n-1)  }}}
{{{a[5] = 2*(-2)^(n-1) = 32 }}}
{{{a[6] = 2*(-2)^(n-1) = -64 }}}
{{{a[7] = 2*(-2)^(n-1) = 128  }}}

{{{sum(  2*(-2)^(n-1) , n=1, 7 )}}}