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.

A102589 Numbers of the forms 4*p or q where both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes.

Original entry on oeis.org

124, 421, 1324, 4231, 13324, 42331, 1333324, 4233331
Offset: 1

Views

Author

Farideh Firoozbakht, Jan 22 2005

Keywords

Comments

This sequence is a subsequence of A069514 (If m is in the sequence then sigma(reversal(m)) = reversal(sigma(m))), so see Comments on A069514. There exists only four known n's such that both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes, n=2,3, 4 and 6.

Examples

			124 and 421 are in the sequence because 124=4*31 and both numbers
31=(10^2-7)/3 and 421=(127*10^(2-1)-7)/3 are primes. It seems that
there is no further term.

Crossrefs

Cf. A069514, A102285.

A103110 Numbers n such that (58*100^n - 157)/99 is prime.

Original entry on oeis.org

2, 3, 5, 63, 237, 407, 687, 4413, 5606
Offset: 1

Views

Author

Farideh Firoozbakht, Jan 24 2005

Keywords

Comments

(58*100^A103110-157)/33 is a subsequence of the sequence A069514, so see Comments on A069514. Next term is greater than 6400.
Next term is greater than 15000. - Michael S. Branicky, Mar 22 2023

Crossrefs

Cf. A069514, A102589.

Programs

  • Mathematica
    Do[If[PrimeQ[(58*10^n - 157)/99], Print[n]], {n, 6400}]
  • PARI
    is(n)=ispseudoprime((58*100^n-157)/99) \\ Charles R Greathouse IV, Jun 13 2017
Showing 1-2 of 2 results.

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

Content is available under The OEIS End-User License Agreement.