Question 1059348
.
The sum of the first  n  positive integers is   {{{S(n)}}} = {{{(n*(n+1))/2}}}.


See the lessons 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Arithmetic-progressions.lesson>Arithmetic progressions</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/The-proofs-of-the-formulas-for-arithmetic-progressions.lesson>The proofs of the formulas for arithmetic progressions</A> 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Problems-on-arithmetic-progressions.lesson>Problems on arithmetic progressions</A>  

in this site.


<pre>
First 10 values are

 n      S(n)
-----------
 1 	 1
 2	 3
 3	 6
 4	10
 5	15
 6	21
 7	28
 8	36
 9	45
10	55
</pre>