I sent him the wikipedia article link. It isn't too difficult to surprise oneself with a pretty good rudimentary approach along lines of the inclusion-exclusion principle, though it won't match best current methods and results (with, I believe, a similar basis).

Jim

On Fri Aug 5th, 2011 9:07 PM EDT John wrote:

>Some Greek chap from long ago worked out a way, but I suppose there are others.

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>--- In primenumbers@yahoogroups.com, Mahmoud Hafiane <mahmoudhafiane@...> wrote:

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>> I joined just to inform you that I can calcolate ordinal number of a prime number.. did someone had done it before?. do you consider this kind of calculation important ?

>> about my claim I affirm that my tecnica to calcolate the ordinal number of a prime number could be considered an empty tautology.. because I calcolate what I know before.. but what is to be considered is that tecnica makes all prime numbers chianed and connected ... exemple to calcolate the ordinal number of 7 in the series of prime numbers I should know a calculation of two chains of numbers..7 is the forth in the order of prime numbers .. but how can we find 4?.. it seems simple isn't.

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