A naive way of attacking the problem is to add up as many terms as you can and see what you get. The problem with the Basel sum, however, is that it converges very slowly. Adding up the first 1000 terms (which would be an extremely arduous task by hand) only gives you a result that is correct in the first two decimal places, but differs in the third. Good approximations, therefore, required some mathematical trickery. "So much work has been done on the [sum] that it seems hardly likely that anything new may still turn up," wrote Euler in a letter. "I, too, in spite of repeated efforts, could achieve nothing more than approximate values ...