The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 19 17:58 EDT 2021. Contains 345144 sequences. (Running on oeis4.)