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

A056687 Numbers k such that 50*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

1, 7, 11, 17, 25, 31, 137, 187, 221, 337, 1001, 2743, 6529, 38689, 39463
Offset: 1

Views

Author

Robert G. Wilson v, Aug 10 2000

Keywords

Comments

Also numbers k such that (5*10^(k+1)+31)/9 is prime.

Links

Crossrefs

Cf. A002275, A093403, A099418.

Programs

  • Mathematica
    Do[ If[ PrimeQ[50*(10^n - 1)/9 + 9], Print[n]], {n, 0, 5000}]

Formula

a(n) = A099418(n) - 1.

Extensions

6529 from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
38689 and 39463 from Serge Batalov, Jan 06 2009 confirmed as next terms by Ray Chandler, Feb 20 2012
Showing 1-2 of 2 results.

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