If you want an old paper with a summation symbol, you could do worse than the book where the symbol was first used, by Euler: http://www.math.dartmouth.edu/~eul

If you want an old paper with a summation symbol, you could do worse than the book where the symbol was first used, by Euler: http://www.math.dartmouth.edu/~euler/docs/originals/E212sec1ch1.pdf http://www.math.dartmouth.edu/~euler/docs/originals/E212sec1... (He uses x as the index variable there.)