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%I #13 Jun 27 2022 01:11:24
%S 97,991,9941,99881,999983,9999971,99999643,999999761,9999999511,
%T 99999999977,999999998863,9999999998633,99999999998333,
%U 999999999999877,9999999999998633,99999999999987443,999999999999999331,9999999999999988633,99999999999999999631
%N Largest n-digit emirp (A006567) with nonincreasing digits.
%H Michael S. Branicky, <a href="/A127828/b127828.txt">Table of n, a(n) for n = 2..527</a>
%t nde[n_]:=Module[{p=NextPrime[10^n,-1]},While[Max[Differences[ IntegerDigits[ p]]]>0 || CompositeQ[IntegerReverse[p]],p=NextPrime[ p,-1]];p]; Array[nde,17,2] (* _Harvey P. Dale_, Mar 13 2020 *)
%o (Python)
%o from sympy import isprime
%o from itertools import count, islice, combinations_with_replacement as mc
%o def bgen(d):
%o nd = ("".join(m) for m in mc("987654321", d))
%o yield from filter(isprime, map(int, nd))
%o def ok(ndp):
%o s = str(ndp)
%o return len(set(s)) != 1 and isprime(int(s[::-1]))
%o def agen():
%o yield from (next(filter(ok, bgen(d))) for d in count(2))
%o print(list(islice(agen(), 20))) # _Michael S. Branicky_, Jun 26 2022
%Y Cf. A006567, A030540, A114019, A127748, A127827.
%K nonn,base
%O 2,1
%A _Ray Chandler_, Jan 31 2007
%E a(19) and beyond from _Michael S. Branicky_, Jun 26 2022
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