[seqfan] Another "interpret this sequence!" brainteaser
Charles Greathouse
charles.greathouse at case.edu
Mon Aug 2 23:53:56 CEST 2010
A140532 is "a(n) = number of n-digit pandigital primes." In the
examples, it considers all primes below 100 *except* 11 to be
pandigital.
The first interpretation that came to mind was that the sequence was
counting primes without repeated digits. But this gives |{103, ...,
983}| = 97 for a(3), while the sequence has 83. (There are 143
3-digit primes, so it's leaving out 60.)
Any ideas? The sequence cites
Clifford A. Pickover, Wonders of Numbers.
Schaum's Outlines, Combinatorics, see inclusion/exclusion principle
as references, but I don't think the sequence appears in either, based
on a Google Book search.
Charles Greathouse
Analyst/Programmer
Case Western Reserve University
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