16th April
On this day in 1673, Leibniz wrote to Oldenburg about series:-
I conjecture that Mr Collins himself does not speak of these summations of infinite series because he brings forward the example of the series which if it is continued to infinity cannot be summed because the sum is not finite, like the sum of the triangular numbers, but infinite. But now I am cramped by the space of my paper.On this day in 2009 Google released a Huygens doodle (two days late).