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 1-3 of 3 results.

A099422 Numbers k such that 8*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

1, 2, 3, 5, 8, 9, 15, 51, 71, 77, 224, 296, 315, 2090, 2906, 3395, 3882, 5114, 6056, 7254, 7995, 18173, 18971, 35006, 69674, 175428, 253313
Offset: 1

Views

Author

Robert G. Wilson v, Oct 14 2004

Keywords

Comments

Also numbers k >= 1 such that (8*10^k - 53)/9 is prime.
a(26) > 10^5. - Robert Price, Oct 31 2014

Links

Crossrefs

Cf. A002275, A056664, A056694, A093166.

Programs

  • Magma
    [n: n in [1..500] | IsPrime((8*10^n-53) div 9)]; // Vincenzo Librandi, Nov 01 2014
  • Mathematica
    Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 5], Print[n]], {n, 1, 5000}]

Formula

a(n) = A056694(n) + 1.

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(22)-a(25) from Robert Price, Oct 31 2014
a(1)=0 removed by Georg Fischer, Jan 03 2021
a(26)-a(27) from Kamada data by Tyler Busby, Apr 16 2024

A092675 Primes of the form 80*R_k + 1, where R_k is the repunit (A002275) of length k.

Original entry on oeis.org

881, 8888888888888888881, 8888888888888888888888888888888888888888888888888888888888888888888888888888881
Offset: 1

Views

Author

Rick L. Shepherd, Mar 02 2004

Keywords

Comments

Primes of the form 888...881.
The number of 8's in each term is given by the corresponding term of A056664 and so the first term too large to include above is 888...8881 (with 138 8's).
Primes of the form (8*10^k - 71)/9. - Vincenzo Librandi, Nov 16 2010

Links

Crossrefs

Cf. A056664 (corresponding k).
Cf. A051200, A004022, A093176, A093177, A089346, A093174, A092571.

Programs

  • Mathematica
    Select[Table[10 FromDigits[PadRight[{},n,8]]+1,{n,150}],PrimeQ] (* Harvey P. Dale, Aug 07 2019 *)

A099421 0 together with numbers k such that 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

0, 3, 19, 79, 139, 223, 463, 544, 1096, 1419, 3247, 3877, 4417, 9507, 11091, 14602, 27811, 29188, 106729, 188308
Offset: 1

Views

Author

Robert G. Wilson v, Oct 14 2004

Keywords

Comments

Also numbers k such that abs(8*10^k - 71)/9 is a prime.
a(19) > 10^5. - Robert Price, Sep 06 2014

Links

Crossrefs

Cf. A002275, A056664.

Programs

  • Mathematica
    Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 7], Print[n]], {n, 0, 15000}]
  • PARI
    for(n=0,10^4,if(ispseudoprime(abs(8*(10^n-1)/9-7)),print1(n,", "))) \\ Derek Orr, Sep 06 2014

Formula

a(n) = A056664(n-1) + 1.

Extensions

a(17)-a(18) from Kamada data by Robert Price, Sep 06 2014
a(19)-a(20) from Kamada data by Tyler Busby, Apr 30 2024
Showing 1-3 of 3 results.

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

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