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.

A093165 Primes of the form 70*R_k + 3, where R_k is the repunit (A002275) of length k.

Original entry on oeis.org

3, 73, 773, 77773, 777777773, 777777777773, 777777777777773, 777777777777777777773
Offset: 1

Views

Author

Rick L. Shepherd, Mar 26 2004

Keywords

Comments

Primes of the form (7*10^k - 43)/9. - Vincenzo Librandi, Nov 16 2010
The next term, a(9), has 264 digits. - Harvey P. Dale, Jul 19 2012

Links

Crossrefs

Cf. A056689 (corresponding k), A099420.

Programs

  • Mathematica
    Select[Table[FromDigits[PadLeft[{3},n,7]],{n,500}],PrimeQ] (* Harvey P. Dale, Jul 19 2012 *)

A099420 Numbers k such that 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

1, 2, 3, 5, 9, 12, 15, 21, 264, 383, 2720, 4494, 21167, 45825, 55851, 64568, 70727
Offset: 1

Views

Author

Robert G. Wilson v, Oct 14 2004

Keywords

Comments

Also numbers k such that (7*10^k - 43)/9 is prime.
a(18) > 10^5. - Robert Price, Oct 19 2014

Links

Crossrefs

Cf. A002275, A056689, A093165.

Programs

  • Mathematica
    Do[ If[ PrimeQ[ 7(10^n - 1)/9 - 4], Print[n]], {n, 0, 5000}]

Formula

a(n) = A056689(n) + 1.

Extensions

a(13)-a(17) from Robert Price, Oct 19 2014
Showing 1-2 of 2 results.

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

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