A276461 Prime numbers whose digits are k+1 1's and k 2's for some k >= 1.

211, 12211, 21121, 21211, 22111, 1121221, 1212121, 2121121, 2211211, 2221111, 111221221, 112212211, 112221211, 121211221, 211122211, 211212121, 211222111, 221112121, 221212111, 11122121221, 11122221211, 11211221221, 11212211221, 11212221121, 11222112211

Offset

1,1

Comments

The sequence is conjectured to be infinite.

Links

Table of n, a(n) for n=1..25.

Mathematica

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 *)

Prog

(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

Crossrefs

Cf. A000040, A020450.

Sequence in context: A289983 A212851 A069425 * A093732 A116075 A276462

Adjacent sequences: A276458 A276459 A276460 * A276462 A276463 A276464

Keyword

nonn,base

Author

Bob Selcoe, Sep 03 2016

Status

approved