|
|
A334170
|
|
Emirps containing only the digits 1 and 2.
|
|
1
|
|
|
111211, 112111, 12122221, 12222121, 1111122121, 1212211111, 11121211121, 11212221121, 12111212111, 12112221211, 111122221121, 111122222111, 111122222221, 111211221221, 111212212211, 111212222111, 111222212111, 111222221111, 112111211221, 112122112211, 112122211121
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
MATHEMATICA
|
Union @ Flatten @ Table[FromDigits /@ Select[Tuples[{1, 2}, n] , PrimeQ @ (m = FromDigits[#]) && # != (r = Reverse[#]) && PrimeQ @ FromDigits[r] &], {n, 12}] (* Amiram Eldar, Apr 18 2020 *)
Table[Select[FromDigits/@Tuples[{1, 2}, n], !PalindromeQ[#]&&AllTrue[ {#, IntegerReverse[ #]}, PrimeQ]&], {n, 12}]//Flatten (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Nov 08 2020 *)
|
|
PROG
|
(PARI) isok(p) = if (isprime(p), my(d=digits(p), rd=Vecrev(d)); (vecsort(d, , 8) == [1, 2]) && isprime(fromdigits(rd)) && (rd != d));
lista(nn) = {for (n=1, nn, my(vf = vector(n, k, 1)); for (i=1, 2^n-1, my(vpos = select(x->(x==1), Vecrev(binary(i)), 1), nvf = vf); for (i=1, #vpos, nvf[vpos[i]] = 2; ); my(x = eval(Str(1, fromdigits(Vecrev(nvf)), 1))); if (isok(x), print1(x, ", ")); ); ); } \\ Michel Marcus, Apr 18 2020
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|