[seqfan] Re: Most efficient way to construct a list of pandigital palindromic numbers?
Alonso Del Arte
alonso.delarte at gmail.com
Tue Dec 8 05:25:52 CET 2009
Douglas's quote of 78695 to the list matches Hans's in an e-mail he sent me
earlier.
As for the 20-digit members of the sequence, I am certain the explanation is
very simple and I would have enough room to write it here if I knew it.
Al
On Mon, Dec 7, 2009 at 11:12 PM, Hans Havermann <pxp at rogers.com> wrote:
> Douglas McNeil:
>
> > Does Mma have an idiom for permutations equivalent to python iterators
> > which step through a loop without constructing it?
>
> I don't know Python but 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, and UnrankPermutation[n,l] (it was
> NthPermutation[n,l] in older versions of Mathematica) which gives the
> n-th permutation in the lexicographic list of permutations of list l.
>
> > (For the record, I find 78695 19-digit numbers.)
>
> Quick, how many 20-digit numbers? ;)
>
>
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