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A047814 Largest prime substring of n, or 0 if no such substring exists.

%I A047814 #22 Dec 29 2023 23:18:34
%S A047814 0,0,2,3,0,5,0,7,0,0,0,11,2,13,0,5,0,17,0,19,2,2,2,23,2,5,2,7,2,29,3,
%T A047814 31,3,3,3,5,3,37,3,3,0,41,2,43,0,5,0,47,0,0,5,5,5,53,5,5,5,7,5,59,0,
%U A047814 61,2,3,0,5,0,67,0,0,7,71,7,73,7,7,7,7,7,79,0,0,2,83,0,5,0,7,0,89
%N A047814 Largest prime substring of n, or 0 if no such substring exists.
%C A047814 A211396(n) <= a(n). - _Reinhard Zumkeller_, Feb 08 2013
%H A047814 Reinhard Zumkeller, <a href="/A047814/b047814.txt">Table of n, a(n) for n = 0..10000</a>
%e A047814 a(10)=0, a(1227)=227.
%t A047814 a[n_] := (id = IntegerDigits[n]; lg = Length[id]; sel = Select[ FromDigits /@ Flatten[ Table[ id[[i ;; j]], {i, 1, lg}, {j, i, lg}], 1], PrimeQ]; If[ sel === {}, 0, Last[ Sort[ sel] ] ]); Table[ a[n], {n, 0, 99}] (* _Jean-François Alcover_, Feb 23 2012 *)
%t A047814 lps[m_]:=Max[Select[Flatten[Table[FromDigits/@Partition[ IntegerDigits[ m],n,1],{n,IntegerLength[m]}]],PrimeQ]]; Array[lps,100,0]/. -\[Infinity]->0 (* _Harvey P. Dale_, Feb 26 2014 *)
%o A047814 (Haskell)
%o A047814 import Data.List (isInfixOf)
%o A047814 a047814 n = if null ips then 0 else head ips
%o A047814    where ips = [p | p <- reverse $ takeWhile (<= n) a000040_list,
%o A047814                     show p `isInfixOf` show n]
%o A047814 -- _Reinhard Zumkeller_, Feb 08 2013
%Y A047814 Cf. A211396.
%K A047814 nonn,easy,base,nice,look
%O A047814 0,3
%A A047814 _N. J. A. Sloane_
%E A047814 Corrected (41) by _Jean-François Alcover_, Feb 23 2012