Cesàro ayaa markii hore u tixraacay "formulaska caadiga ah" ee 1 − 2n + 3n − 4n +... sida "isku dheelitirnaan aan macquul ahayn", iyo 1883 Cesàro muujiyay aragtida caadiga ah ee waqtiga in qaaciidooyinka ay ahaayeen been ah laakiin weli si qaab ahaan waxtar leh. Ugu dambeyntii, in uu 1890 Sur la multiplication des séries, Cesàro qaaday hab casri ah laga bilaabo qeexidda. taxanaha ayaa sidoo kale loo bartay qiimaha non-integer of n, kuwaas oo ka dhigi function Dirichlet eta. Qayb ka mid ah dhiirigelinta Euler ee daraasadda taxanaha la xiriira 1 − 2 − 3 + 4... ahaa functional loo siman yahay ee functional ee eta, taas oo keenta in loo siman yahay ee functional zeta.
Sanadkii 1883