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%I #15 Sep 26 2016 22:28:51
%S 211,12211,21121,21211,22111,1121221,1212121,2121121,2211211,2221111,
%T 111221221,112212211,112221211,121211221,211122211,211212121,
%U 211222111,221112121,221212111,11122121221,11122221211,11211221221,11212211221,11212221121,11222112211
%N Prime numbers whose digits are k+1 1's and k 2's for some k >= 1.
%C The sequence is conjectured to be infinite.
%t Table[Select[Map[FromDigits, Permutations[ConstantArray[1, n + 1] ~Join~ ConstantArray[2, n], {2 n + 1}]], PrimeQ], {n, 5}] // Flatten (* _Michael De Vlieger_, Sep 04 2016 *)
%o (PARI) listp(nn) = { forprime(p=2, nn, d = digits(p); if ((vecmin(d) == 1) && (vecmax(d) == 2) && (#select(x->x==1, d) == #select(x->x==2, d) +1), print1(p, ", ");););} \\ _Michel Marcus_, Sep 04 2016
%Y Cf. A000040, A020450.
%K nonn,base
%O 1,1
%A _Bob Selcoe_, Sep 03 2016
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