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
KEYWORD
nonn,base
AUTHOR
Amiram Eldar, Jan 23 2020
STATUS
approved