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.

A178321 Numbers k such that 58/111*(10^(3*k)-1)-1 is prime.

Original entry on oeis.org

1, 2, 15, 74, 278, 541, 668, 1320, 1780, 1874, 4824, 13310, 20420, 24887
Offset: 1

Views

Author

Farideh Firoozbakht, May 26 2010

Keywords

Comments

If k is in the sequence then m=3*(58/111*(10^(3*k)-1)-1) is a term of A072394.
Namely if k is a term of this sequence then for m=1/37*(58*10^(3*k)-169) we have sigma(m)=reversal(m)-m (see comment lines of A072394).
There is no further term up to 3000. Numbers corresponding to the larger terms are probable primes.
a(15) > 50000. - Robert Price, Oct 20 2014

Crossrefs

Cf. A072394, A178322.

Programs

  • Mathematica
    Do[If[PrimeQ[58/111*(10^(3 n) - 1) - 1], Print[n]], {n, 1874}]

Extensions

a(11)-a(14) from Robert Price, Oct 20 2014

A178322 Numbers n such that 156/101*(10^(4n)-1)-1 is prime.

Original entry on oeis.org

1, 2, 5, 29, 30, 108, 679, 4478, 8736, 17000, 22427, 22731
Offset: 1

Views

Author

Farideh Firoozbakht, May 26 2010

Keywords

Comments

If n is in the sequence then m=91*(156/101*(10^(4n)-1)-1) is a term of A072394. Namely if n is a term of this sequence then for m=1/101*(14196*10^(4n)-23387), we have sigma(m)=reversal(m)-m (see comment lines of A072394).
Numbers corresponding to the larger terms are probable primes.
Next term exceeds 3500. - Robert G. Wilson v, Aug 08 2011.
a(13) > 40000. - Robert Price, May 23 2014

Crossrefs

Cf. A072394, A178321.

Programs

  • Mathematica
    Select[Range[700], PrimeQ[156/101*(10^(4 #) - 1) - 1] &]

Extensions

a(8)-a(12) from Robert Price, May 23 2014
Showing 1-2 of 2 results.

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