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.

A122691 a(n) is the least prime factor of (9 * 10^(6*n-4) - 11) / 7.

Original entry on oeis.org

127, 401, 19, 53, 151, 7, 139, 127, 19, 78721, 3458771, 19, 7, 38954263, 19, 79, 53, 19, 157, 7, 19, 127, 18191, 19, 12119, 421, 7, 107434435760557861791327959267859939351202240879711219728393537522815146155523913, 79, 19, 23196834569628410341642097660316821
Offset: 1

Views

Author

Zak Seidov, Sep 22 2006

Keywords

Examples

			n=2, (9*10^8-11)/7 = 128571427 = 401 * 320627 hence a(2)=401.

Links

Crossrefs

Cf. A100275, A122862.

Extensions

a(28) onward corrected by Sean A. Irvine, May 25 2024

A122862 Numbers k such that (9*10^k - 11)/7 is prime.

Original entry on oeis.org

2, 260, 650, 1928, 5768, 36548
Offset: 1

Views

Author

Zak Seidov, Sep 22 2006

Keywords

Comments

All terms are of the form 2+6*i, i = 0,1,... .
Are there any k's such that (9*10^k - 11)/p is prime for prime p<>7?

Crossrefs

Cf. A100275.

Programs

  • Mathematica
    Do[If[PrimeQ[(9*10^n-11)/7],Print[n]],{n,2,7220,6}]
  • PARI
    is(n)=ispseudoprime((9*10^n-11)/7) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(6) from Michael S. Branicky, Jul 08 2025

A111023 Integers n such that 9*10^n + 11 is a prime number.

Original entry on oeis.org

1, 2, 3, 4, 6, 8, 16, 20, 27, 115, 180, 274, 576, 1111, 2404, 5127, 8082, 9514, 12808, 14752, 15926, 22670, 37432, 41988, 53707, 72595, 92742
Offset: 1

Views

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 04 2005

Keywords

Comments

See Kamada link - primecount.txt for terms, primesize.txt for discovery details including probable or proved primes - search on "90w11".
a(28) > 10^5. - Robert Price, Jan 28 2017

Examples

			n = 6 is a member because 9*10^6 + 11 = 9*1000000 + 11 = 9000011, which is prime.

Links

Crossrefs

Cf. A100275 = numbers n such that 9*10^n-11 is prime.
Cf. A049054, A088274, A088275, A095688, A107083, A108049, A108050, A108052, A108054, A110980.

Programs

  • Mathematica
    Do[If[PrimeQ[9*10^n+11],Print[n]],{n,1,1300}] (* Zak Seidov, Sep 14 2006 *)

Extensions

Edited by N. J. A. Sloane, Apr 11 2008
a(16)-a(22) from Ray Chandler, Dec 23 2010
a(23)-a(27) from Robert Price, Jan 28 2017
Showing 1-3 of 3 results.

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

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