a1+a2+a3+…+a2007
=(2+2008)*(2007)/2
=2*1004^2
=2016032错了a1+a2+a3+....+a2007
=2+3+4+ ....+2008
=(2008+2)* 2007/2
=2010* 2007/2
=1005*2007
=2017035(⊙o⊙)…，保证对么en