Find the sum of the integers from - 2007 through + 2009

This is an arithmetic sequence with first term - 2007 and common difference of 1. and last term = 2009. Total number of terms = 2008 + 2009 = 4017

Sn = (n/2) (a + l)

Sum (4017/2) (-2007 + 2009) = 4017 * 2 / 2 = 4017 Answer