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.

Showing 1-2 of 2 results.

A099418 Numbers k such that 5*R_k + 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

2, 8, 12, 18, 26, 32, 138, 188, 222, 338, 1002, 2744, 6530, 38690, 39464, 335480, 343734
Offset: 1

Views

Author

Robert G. Wilson v, Oct 14 2004

Keywords

Comments

Also numbers k such that (5*10^k + 31)/9 is prime.

Links

Crossrefs

Cf. A002275, A093403, A056687.

Programs

  • Mathematica
    Do[ If[ PrimeQ[ 5(10^n - 1)/9 + 4], Print[n]], {n, 0, 5000}]

Formula

a(n) = A056687(n) + 1.

Extensions

a(13)-a(15) from Kamada link by Ray Chandler, Feb 27 2012
a(16)-a(17) from Kamada data by Tyler Busby, May 03 2024

A093403 Primes of the form 50*R_k + 9, where R_k is the repunit (A002275) of length k.

Original entry on oeis.org

59, 55555559, 555555555559, 555555555555555559, 55555555555555555555555559, 55555555555555555555555555555559
Offset: 1

Views

Author

Rick L. Shepherd, Mar 28 2004

Keywords

Comments

Primes of the form (5*10^k + 31)/9. - Vincenzo Librandi, Nov 17 2010

Links

Crossrefs

Cf. A056687 (corresponding k), A099418.

Formula

a(n) = (50*10^A056687(n) + 31)/9 = (5*10^A099418(n) + 31)/9.

Extensions

Edited by Ray Chandler, Feb 27 2012
Showing 1-2 of 2 results.

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