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A276462 Prime numbers that consist of k 2's digits followed by k+1 1's digits for some k >= 1. 0
211, 22111, 2221111, 22222222222222222222222222111111111111111111111111111, 2222222222222222222222222222222221111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(4) is 26 2's followed by 27 1's; a(5) is 33 2's followed by 34 1's.

The sequence is conjectured to be infinite.

Let b(n) be the sequence of corresponding k's. b(1)-b(8) are 1, 2, 3, 26, 33, 215, 259, 799. - Felix Fröhlich, Sep 04 2016

LINKS

Table of n, a(n) for n=1..5.

MATHEMATICA

Select[FromDigits@ Join[ConstantArray[2, #], ConstantArray[1, # + 1]] & /@ Range@ 36, PrimeQ] (* Michael De Vlieger, Sep 04 2016 *)

PROG

(PARI) a002275(n) = (10^n-1)/9

a011557(n) = 10^n

terms(n) = my(i=0, k=1); while(1, my(x=2*a002275(k)*a011557(k+1)+a002275(k+1)); if(ispseudoprime(x), print1(x, ", "); i++); k++; if(i==n, break))

/* Print initial five terms as follows: */

terms(5) \\ Felix Fröhlich, Sep 04 2016

CROSSREFS

Cf. A000040 (prime numbers).

Sequence in context: A276461 A093732 A116075 * A096834 A013547 A181002

Adjacent sequences:  A276459 A276460 A276461 * A276463 A276464 A276465

KEYWORD

nonn,base

AUTHOR

Bob Selcoe, Sep 03 2016

STATUS

approved

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Last modified August 17 17:05 EDT 2018. Contains 313816 sequences. (Running on oeis4.)