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.

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A175727 Numbers k such that both A000203(k)-k-1 and A000203(k)-2*k-1 are prime numbers.

Original entry on oeis.org

30, 42, 60, 70, 78, 102, 138, 186, 198, 216, 222, 228, 240, 246, 258, 270, 282, 360, 372, 390, 414, 438, 492, 498, 546, 582, 600, 606, 642, 708, 720, 756, 762, 774, 786, 810, 852, 870, 930, 942, 954, 1002, 1014, 1020, 1026, 1038, 1068, 1086, 1182, 1266, 1290
Offset: 1

Views

Author

Max Alekseyev, Aug 18 2010

Keywords

Comments

A simpler version of A179945, added at the request of the editor-in-chief.

Crossrefs

Subsequence of A179945.
Cf. A000203.

Programs

  • Maple
    q:= n-> (t-> andmap(isprime, [t-n-1, t-2*n-1]))(numtheory[sigma](n)):
select(q, [$1..1500])[];  # Alois P. Heinz, Mar 21 2023
  • PARI
    is(n)=my(s=sigma(n)); isprime(s-n-1) && isprime(s-n-n-1) \\ Charles R Greathouse IV, Feb 19 2013

Extensions

Edited by N. J. A. Sloane, Aug 28 2010

A180268 Numbers n, not divisible by 3, 5, 7 or 11, such that A000203(n)-n-1 and 2*n+1-A000203(n) are prime numbers.

Original entry on oeis.org

4, 988, 1612, 3172, 5332, 7852, 11908, 18748, 19276, 21268, 21508, 25156, 32188, 35932, 41116, 41452, 43108, 50236, 54436, 55876, 57412, 62452, 65836, 71248, 72748, 74572, 85828, 88996, 96772, 97708, 99292, 103948, 104956, 105772, 110812, 116356, 116428
Offset: 1

Views

Author

Alexey Galkin (fetch91(AT)gmail.com), Aug 23 2010

Keywords

Crossrefs

Cf. A157449, A175727 and A179945.

Extensions

Divisibility requirement added to definition to match the sequence; 4 and terms beyond 7852 added - R. J. Mathar, Aug 25 2010
Showing 1-2 of 2 results.

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

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