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 A331486 Numbers k which are emirps in more bases 1 < b < k than any previous number. 2
 2, 5, 7, 11, 13, 17, 23, 29, 31, 41, 43, 53, 67, 73, 79, 97, 113, 127, 157, 193, 223, 269, 277, 311, 379, 421, 431, 467, 487, 563, 613, 647, 743, 907, 937, 977, 1093, 1193, 1249, 1259, 1373, 1483, 1543, 1637, 1667, 1933, 2239, 2393, 2477, 2521, 2857, 2957, 3083 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The corresponding numbers of bases are 0, 1, 3, 6, 8, 9, 12, 13, 17, 21, 24, ... (see the link for more values). LINKS Amiram Eldar, Table of n, a(n) for n = 1..175 Amiram Eldar, Table of n, a(n), number of bases for n = 1..175 EXAMPLE 2 is not emirp in any base. 5 is emirp in one base, 3: 5 is 12 in base 3, and 21 in base 3 is 7 which is also a prime. 7 is emirp in 3 bases, 3, 4, and 5. MATHEMATICA emirpQ[n_, b_] := n != (rev = FromDigits[Reverse @ IntegerDigits[n, b], b]) && And @@ PrimeQ[{n, rev}]; emirpCount[n_] := Length @ Select[Range[2, n - 1], emirpQ[n, #] &]; seq = {}; emax = -1; Do[e1 = emirpCount[n]; If[e1 > emax, emax = e1; AppendTo[seq, n]], {n, 2, 3000}]; seq CROSSREFS Cf. A006567, A080790, A087911, A107129, A228768. Sequence in context: A228200 A245063 A168033 * A257974 A323782 A020591 Adjacent sequences: A331483 A331484 A331485 * A331487 A331488 A331489 KEYWORD nonn,base AUTHOR Amiram Eldar, Jan 23 2020 STATUS approved

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Last modified June 10 17:56 EDT 2023. Contains 363206 sequences. (Running on oeis4.)