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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A091454 Integers k such that 3*phi(k) < k.

Original entry on oeis.org

30, 42, 60, 66, 78, 84, 90, 102, 114, 120, 126, 132, 138, 150, 156, 168, 174, 180, 186, 198, 204, 210, 222, 228, 234, 240, 246, 252, 258, 264, 270, 276, 282, 294, 300, 306, 312, 318, 330, 336, 342, 348, 354, 360, 366, 372, 378, 390, 396, 402, 408, 414, 420
Offset: 1

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Author

Robert G. Wilson v, Jan 10 2004

Keywords

Comments

If k is present so are all m*k, m>1.
The smallest odd number in this sequence is 111546435 = 3*5*7*11*...*23. - T. D. Noe, Jan 15 2004

Links

Crossrefs

Cf. A000010 (phi), A054741, A066765, A091456.

Programs

  • Magma
    [k:k in [1..500]|3*EulerPhi(k) lt k]; // Marius A. Burtea, Jan 13 2020
  • Maple
    filter:= n -> 3*numtheory:-phi(n) < n:
select(filter, [$1..10000]); # Robert Israel, Jan 13 2020
  • Mathematica
    Select[ Range[437], 3EulerPhi[ # ] < # & ]
  • PARI
    is(n) = 3*eulerphi(n) < n; \\ Amiram Eldar, Apr 07 2024
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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