Question 812881
This series consists of consecutive integers, but the sign alternates.  
-1 raised to an even power is +1 and -1 raised to an odd power is -1.  So the following summation notation will reproduce the given series:
{{{sum( (-1)^(n+1) * n, n=1, 50)}}}
Check:
The 1st term is {{{(-1)^2*1 = 1}}}
The 2nd term is {{{(-1)^3*2 = -2}}}
and so on...