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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A096209 Primes of the form 10 followed by 9's only.

Original entry on oeis.org

109, 10999999999, 1099999999999, 1099999999999999999, 109999999999999999999999, 1099999999999999999999999999999, 10999999999999999999999999999999999999
Offset: 1

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Author

Cino Hilliard, Jul 28 2004

Keywords

Comments

Or, primes of the form 10^k + 10^(k-1) - 1.
Number of 9's in a(n) is given by A111391(n). - Daniel Starodubtsev, Jan 06 2020

Crossrefs

Cf. A111391, A113628, A113629, A113630.
Primes in A198700.

Programs

  • Mathematica
    t = {}; Do[m = n; p = 10^(n + 1) + (10^n - 1); If[PrimeQ[p], AppendTo[t, p]], {n, 165}]; t (* Robert G. Wilson v *)
  • PARI
    f(n) = for(x=1,n,y=10^x+10^(x-1)-1;if(ispseudoprime(y),print1(y", ")))

Formula

a(n) = 11*10^A111391(n) - 1 = A198700(A111391(n)). - Elmo R. Oliveira, Jun 14 2025

Extensions

Entry revised by N. J. A. Sloane, Apr 01 2006
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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