cp's OEIS Frontend

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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A056654 Numbers k such that 10*R_k + 3 is prime, where R_k is the repunit (A002275) of length k.

Original entry on oeis.org

0, 1, 2, 4, 8, 10, 23, 83, 220, 1313, 2951, 20015, 51053
Offset: 1

Views

Author

Robert G. Wilson v, Aug 09 2000

Keywords

Comments

Also numbers k such that (10^(k+1)+17)/9 is prime.
a(14) > 10^5. - Robert Price, Nov 01 2014

Examples

			8 is a term because 111111113 is a prime.

Links

Crossrefs

Cf. A093011 (corresponding primes), A097683.

Programs

  • Mathematica
    Do[ If[ PrimeQ[ 10*(10^n - 1)/9 + 3 ], Print[ n ] ], {n, 0, 1350} ]
  • PARI
    is(n)=ispseudoprime(10^n\9*10+3) \\ Charles R Greathouse IV, Nov 10 2021

Formula

a(n) = A097683(n+1) - 1. - Robert Price, Nov 01 2014

Extensions

a(11) (only a probable prime) from Rick L. Shepherd, Mar 14 2004
a(12)-a(13) derived from A097683 by Robert Price, Nov 01 2014

A095680 13, together with primes of the form 10^k + 13 for some k >= 0.

Original entry on oeis.org

13, 113, 1013, 100000000000000013, 10000000000000000000000013, 1000000000000000000000000000000000000000000000000000000000000000000000000000000013
Offset: 1

Views

Author

Xavier Bury (x(AT)monsieurx.com), Jul 04 2004

Keywords

Comments

The next term has 141 digits. - Harvey P. Dale, May 26 2024

Crossrefs

See A095688 for the values of k.
Cf. A093011.

Programs

  • Mathematica
    Join[{13},Select[Table[FromDigits[PadRight[{1},n,0]]+13,{n,100}],PrimeQ]] (* Harvey P. Dale, May 26 2024 *)

Extensions

Corrected by N. J. A. Sloane, Dec 31 2016 at the suggestion of Harvey P. Dale.
Corrected by Harvey P. Dale, May 26 2024
Showing 1-2 of 2 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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