Make your program sequential!
Python 2, 35 Bytes

I decided to use the obvious sequence A000027, which essentially has the formula n ;) If you run the following code:



#print'n'
n=1
exec'print n;n+=1;'*8


You get the output:

1
2
3
4
5
6
7
8


And if you take the 8 characters from my source code (0-indexed), you get this:

print'n'


Which simply prints n.



If you were hoping for a more exciting answer, here's a Python 2 solution for n^2, i.e. A000290:

#p  r    i      n        t          '            n              ^                2                  '
n=1
exec'print n*n;n+=1;'*10