Question 1150896
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In your post, &nbsp;it should be &nbsp;<U>EITHER</U>&nbsp; comma between &nbsp;(2y+1) &nbsp;and &nbsp;10,  &nbsp;<U>OR</U>&nbsp; the multiplication sign.


But not the &nbsp;"blank space", &nbsp;which violates the logic of your post and makes the problem/(the post) &nbsp;<U>non-sensical</U>. 



Also, do not consider the &nbsp;"solution"&nbsp; by @ankor@dixie-net.com &nbsp;seriously, 

since in his first line formula he uses &nbsp;INCORRECT&nbsp; total number of terms in the sequence.