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Jun 23 at 21:08 vote accept thefool
Jun 16 at 18:44 comment added thefool @Henry does my answer look correct?
Jun 16 at 18:44 answer added thefool timeline score: 1
Jun 16 at 18:16 comment added thefool Ok, now I understand. Thank you for help. I will update my original question or write an answer containing the use of inclusion-exclusion to bring it home. Thanks!
Jun 16 at 18:01 comment added Henry @thefool You do not need Stirling numbers of second kind to find the values $p(52,52)\approx 4.7\times 10^{-22}$ or $p(225,52)\approx 0.50579$ or $p(1000,52)\approx 0.9999998$; you can use a spreadsheet to get all these values simultaneously. But an exact compact expression will require Stirling numbers of the second kind or something equivalent.
Jun 16 at 17:48 comment added thefool @Henry, so the answer is: $p(N, 52) = p(N-1, 52) + \frac{1}{52} p(N-1, 51)$ and it is impossible to solve that recoursion (express it as a compact function of N) without Stirling numbers of second kind?
Jun 16 at 17:43 comment added Henry @thefool: you want $P(N,52)$ for all the cards - in the linked recursion answer $P(N,365)$ for all the $365$ days to be somebody's birthday. "Unfolding" may not be the best approach; starting with $m=0$ and then increasing towards $52$ may be more efficient. If you want to avoid sums (i.e. reject recursion or inclusion-exclusion) then exact results and compact expressions require Stirling numbers of the second kind or something equivalent.
Jun 16 at 17:39 comment added thefool Should I therefore unfold the recoursion for $m = 52$ and 'go down with m' until $m = 0$? That will be my function of N, right?
Jun 16 at 17:30 comment added thefool @Henry I see the recursion.If I replace 365 days with 52 cards I get: $p(N,m) = \frac{m}{52}p(N-1,m)+\frac{53-m}{52}p(N-1,m-1)$. But that is a recoursion on $N$ and $m$. In my case, I need compact function of $N$ (not including sums).
Jun 16 at 5:20 comment added user2661923 See this article for an introduction to Inclusion-Exclusion. Then, see this answer for an explanation of and justification for the Inclusion-Exclusion formula.
Jun 16 at 3:24 history edited RobPratt
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Jun 16 at 1:57 comment added Henry My answer to the linked question gives a recursion if you replace $365$ days with $52$ cards. For an example of inclusion-exclusion see math.stackexchange.com/a/4813267/6460 using $m=52$
Jun 16 at 1:27 comment added thefool @Henry thank you for help! Could you show me the inclusion-exclusion and recursion ideas? Provided link and the answer mention Stirling numbers of second kind and I would love to avoid those.
Jun 16 at 0:21 comment added Henry The answer is $\dfrac{52!\, S_2(N,52)}{52^N}$ where $S_2(N,52)$ is a Stirling number of the second kind. You can also use inclusion-exclusion or recursion to find it. math.stackexchange.com/questions/4506194/… is one of many similar questions on this site.
Jun 16 at 0:08 history asked thefool CC BY-SA 4.0