x+4x+7x+10x+…+2008x
=x(1+4+7+...+2008)
1,4,7...2008是个等差数列
项数为：(2008-1)÷3+1=670
1+2+3+.+2008
=（1+2008）×670÷2
=673015
原式=673015x