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.

A144737 Numbers A141426(k) such that the three numbers A141426(k) -/+ 5 and A141426(k) + 1 are all prime.

Original entry on oeis.org

18, 42, 78, 108, 162, 228, 312, 378, 438, 462, 738, 756, 858, 882, 1092, 1302, 1428, 1488, 1548, 1998, 2292, 2346, 2388, 2472, 2688, 2856, 3186, 3318, 3612, 3696, 4446, 4518, 4728, 4788, 4998, 5232, 5526, 5568, 5688, 5856
Offset: 1

Views

Author

Giovanni Teofilatto, Sep 20 2008

Keywords

Crossrefs

Cf. A141427.

Extensions

More terms from R. J. Mathar, Aug 23 2010

A141427 a(n) = phi(A067775(n)).

Original entry on oeis.org

1, 4, 10, 16, 22, 28, 30, 40, 46, 52, 58, 60, 70, 72, 82, 88, 100, 106, 112, 130, 136, 138, 148, 150, 156, 166, 172, 178, 180, 190, 196, 198, 210, 226, 232, 238, 240, 250, 256, 262, 268, 270, 280, 282, 292, 310, 316, 330, 336, 346, 352, 358, 366, 372, 382, 388
Offset: 1

Views

Author

Giovanni Teofilatto, Aug 06 2008

Keywords

Comments

Count of numbers smaller than and coprime to p for primes p such that p + 4 is composite.
Subsequence of A006093.

Crossrefs

Cf. A067775, A000010 (Euler totient function), A006093 (primes minus 1), A141426, A141515.

Programs

  • PARI
    {forprime(p=2, 400, if(!isprime(p+4), print1(eulerphi(p), ",")))} \\ Klaus Brockhaus, Aug 31 2008

Extensions

More terms from Robert G. Wilson v, Aug 18 2008
Edited by N. J. A. Sloane and Klaus Brockhaus, Aug 31 2008

A141515 a(n) = phi(A067774(n)) where phi is Euler totient function.

Original entry on oeis.org

1, 6, 12, 18, 22, 30, 36, 42, 46, 52, 60, 66, 72, 78, 82, 88, 96, 102, 108, 112, 126, 130, 138, 150, 156, 162, 166, 172, 180, 192, 198, 210, 222, 228, 232, 240, 250, 256, 262, 270, 276, 282, 292, 306, 312, 316, 330, 336, 348, 352, 358, 366, 372, 378, 382, 388
Offset: 1

Views

Author

Giovanni Teofilatto, Aug 11 2008

Keywords

Comments

Count of numbers smaller than and coprime to p for primes p such that p + 2 is composite.
Subsequence of A006093.

Links

Crossrefs

Cf A067774 (primes p such that p+2 is composite), A000010 (Euler totient function), A006093 (primes minus 1), A141426, A141427.

Programs

  • Magma
    [EulerPhi(p): p in PrimesUpTo(400) | not IsPrime(p+2)]; // Vincenzo Librandi, Feb 09 2018
  • Mathematica
    EulerPhi[#]&@Select[Prime@Range@80, !PrimeQ[# + 2] &] (* Vincenzo Librandi, Feb 09 2018 *)
  • PARI
    {forprime(p=2, 400, if(!isprime(p+2), print1(eulerphi(p), ",")))} \\ Klaus Brockhaus, Aug 31 2008

Extensions

Edited and a(1) = 1, a(12) = 66 inserted by Klaus Brockhaus, Aug 31 2008
Showing 1-3 of 3 results.

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

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