[seqfan] Re: Most efficient way to construct a list of pandigital palindromic numbers?
pxp at rogers.com
Fri Dec 11 15:20:44 CET 2009
> ... I was looking at sequential-permutation operators
> in Mathematica earlier and there are "Combinatorica"
> add-on functions such as NextPermutation[p] which gives
> the permutation following p in lexicographic order...
>> (For the record, I find 78695 19-digit numbers.)
> Quick, how many 20-digit numbers? ;)
A postscript to my above comments and Douglas McNeil's co-calculation
of all 78695 19-digit pandigital palindromic primes. I subsequently
generated all 4232506 21-digit PPPs (89 MB, if anyone is interested).
A 23-digit attempt using Mathematica's Permutations function did not
have enough memory, so I rewrote the program to use that
NextPermutation function and discovered, after some head-scratching,
that NextPermutation does NOT step as expected through all the
Permutations of a list when that list contains multiple items:
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