A new approach on the urn problem : semi-convergent series.



If U_n(a)= 1/(10n-9)^a + 1/(10n-8)^a + 1/(10n-7)^a+...+ 1/(10n-1)^a +1/(10n)^a -1/n^a, U_n(a) simulates the operation at time n of putting ten balls in the urn marked 10n-9,...,10n and of removing ball n, and the sum of series S(a)=sum(U_n(a), n=1..infinity) should give a good idea of what is in the urn "at the end". But in fact, S(a)=0 if a>1, S(1)= ln(10) (a nice exercise, that one) and S(a) diverges (towards +oo) if a<1...
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