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A276461 Prime numbers whose digits are k+1 1's and k 2's for some k >= 1. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 20 17:42 EST 2018. Contains 297961 sequences.