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%I #18 Jan 12 2024 22:46:13
%S 0,2,3,0,5,0,7,0,0,0,11,2,31,41,5,61,71,0,19,2,2,2,23,2,5,2,7,2,29,3,
%T 31,23,3,43,53,3,73,83,3,0,41,2,43,0,5,0,47,0,0,5,5,5,53,5,5,5,7,5,59,
%U 0,61,2,3,0,5,0,67,0,0,7,71,7,73,47,7,67,7,7,97,0,0,2,83,0,5,0,7,0,89,0,19
%N Largest prime which can be formed from digits of n, or 0 if no such prime exists.
%H Robert Israel, <a href="/A101991/b101991.txt">Table of n, a(n) for n = 1..10000</a>
%e a(115)=151 because 151 is the largest prime which can be made from digits {1,1,5}.
%p f:= proc(n) local L,N,d,i,j,S,s,p;
%p L:= convert(n,base,10);
%p N:= nops(L);
%p for d from N to 1 by -1 do
%p S:= sort(combinat:-permute(L,d));
%p for i from nops(S) to 1 by -1 do
%p s:= S[i];
%p p:= add(s[j]*10^(d-j),j=1..d);
%p if isprime(p) then return p fi
%p od od;
%p 0
%p end proc:
%p map(f, [$1..100]); # _Robert Israel_, Jan 10 2024
%t a[n_]:=Max[0, Select[FromDigits/@Permutations[IntegerDigits[n], {1, IntegerLength[n]}], PrimeQ]]; Table[a[n], {n, 91}] (* _James C. McMahon_, Jan 08 2024 *)
%K base,easy,nonn,look
%O 1,2
%A _Zak Seidov_, Jan 29 2005