Question 1090420
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It's the sequence of odd numbers with alternating signs.

The sequence of positive odd integers 1,3,5,7,9,... has general
term  2n-1  (one less than the general term for the even integers, 2n)

To cause the signs to alternate, beginning with the first term being
positive, we must multiply by the factor (-1)<sup>n+1</sup>.  So the 
general term is

t<sub>n</sub> = (-1)<sup>n+1</sup>(2n-1)

Edwin</pre></b></font>