[seqfan] Re: Most efficient way to construct a list of pandigital palindromic numbers?

[Douglas McNeil]

> On 12/7/09, Alonso Del Arte <alonso.delarte at gmail.com> wrote:
>>  ...enough for my purpose, which is to verify the validity of
>>  A168334<http://www.research.att.com/~njas/sequences/A168334> and
>>  perhaps add another four or eight terms.

Does Mma have an idiom for permutations equivalent to python iterators
which step through a loop
without constructing it?

# sage: 19-digit pandigital palindromic primes
perms = permutations_iterator(range(10))
ppps = []
for perm in perms:
    nstr = ''.join(map(str, perm))
    n = int(nstr + nstr[-2::-1]) # 18 dig. if initial 0; but then comp. anyway
    if is_prime(n):
        ppps.append(n)
ppps.sort()

(For the record, I find 78695 19-digit numbers.)


Doug

--
Department of Earth Sciences
University of Hong Kong