Question 1157838
#19:

{{{system(a[6]=-128,r=-2)}}}


General term,  {{{(-2)*2^n}}}



What will be sixth term, or at index 6?
<pre>
1        4
2         -8
3        16
4        -32
5        64
6      -128
</pre>
If you then want term at index 11, just substitute 11 for the general term formula.