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A036229 Smallest n-digit prime containing only digits 1 or 2. 25
2, 11, 211, 2111, 12211, 111121, 1111211, 11221211, 111112121, 1111111121, 11111121121, 111111211111, 1111111121221, 11111111112221, 111111112111121, 1111111112122111, 11111111111112121, 111111111111112111, 1111111111111111111, 11111111111111212121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It is conjectured that such a prime always exists.

a(2), a(19), a(23), etc. are the prime repunits (A004023). a(1000) = (10^n-1)/9 + 111011000010.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..400

Robert G. Wilson v, Comments and first 100 terms

MATHEMATICA

Do[p = (10^n - 1)/9; k = 0; While[ ! PrimeQ[p], k++; p = FromDigits[ PadLeft[ IntegerDigits[k, 2], n] + 1]]; Print[p], {n, 1, 20}]

Table[Min[Select[FromDigits/@Tuples[{1, 2}, n], PrimeQ]], {n, 20}] (* Harvey P. Dale, Feb 05 2014 *)

CROSSREFS

Cf. A036937, A068086.

Sequence in context: A188203 A070256 A020450 * A104337 A283512 A214217

Adjacent sequences:  A036226 A036227 A036228 * A036230 A036231 A036232

KEYWORD

nonn,base,nice

AUTHOR

G. L. Honaker, Jr.

EXTENSIONS

Edited by N. J. A. Sloane and Robert G. Wilson v, May 03 2002

STATUS

approved

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Last modified February 24 18:55 EST 2021. Contains 341584 sequences. (Running on oeis4.)