Answer, let this series be one. According to the laws of the listed data, it is not difficult to see that this series a(n+ 1)-an is a arithmetic progression with an error of 40. Let bn=a(n+ 1)-an, then b 1=20, the tolerance is 40, and BN = 20+(n

Then: a (n+1)-an = 40n-20a (n+1) = an+40n-20.

a 1=8

a2=a 1+40* 1-20

a3=a2+40*2-20

........

an = a(n- 1)+40(n- 1)-20

Add the two sides of the equation:

an=8+40( 1+2+3+....+n- 1)-20(n- 1)=20n^2-40n+28

When an=2008, there are 20n 2-40n+28 = 2008.

n^2-2n-99=0

(n+9)(n- 1 1)=0

N=-9 or n= 1 1.

N is a natural number, so n= 1 1.