A101991 Largest prime which can be formed from digits of n, or 0 if no such prime exists.

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, 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, 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

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(115)=151 because 151 is the largest prime which can be made from digits {1,1,5}.

Maple

f:= proc(n) local L, N, d, i, j, S, s, p;
  L:= convert(n, base, 10);
  N:= nops(L);
  for d from N to 1 by -1 do
    S:= sort(combinat:-permute(L, d));
    for i from nops(S) to 1 by -1 do
      s:= S[i];
      p:= add(s[j]*10^(d-j), j=1..d);
      if isprime(p) then return p fi
  od od;
  0
end proc:
map(f, [$1..100]); # Robert Israel, Jan 10 2024

Mathematica

a[n_]:=Max[0, Select[FromDigits/@Permutations[IntegerDigits[n], {1, IntegerLength[n]}], PrimeQ]]; Table[a[n], {n, 91}] (* James C. McMahon, Jan 08 2024 *)

Crossrefs

Sequence in context: A331097 A047814 A365276 * A296065 A174900 A344369

Adjacent sequences: A101988 A101989 A101990 * A101992 A101993 A101994

Keyword

base,easy,nonn,look

Author

Zak Seidov, Jan 29 2005

Status

approved