Question 1072112
-9,101,-999,10001,-99999?
<pre>

    -9 = -10+1
   101 =  100+1
  -999 = -1000+1
 10001 =  10000+1
-99999 = -100000+1

So it's the powers of 10 with alternating signs, plus 1.

(-1)<sup>n</sup> is the factor that causes the signs to 
alternate:

So the nth term of the sequence is

a<sub>n</sub> = (-1)<sup>n</sup>10<sup>n</sup> + 1

or

a<sub>n</sub> = (-10)<sup>n</sup> + 1

Edwin</pre>