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A127828 Largest n-digit emirp (A006567) with nonincreasing digits.

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