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.

A207575 Numbers k such that phi(k) + 2 divides k + 2 and k is not twice a prime.

Original entry on oeis.org

1, 390, 10374, 2283934267736070, 7316037865689066623729670
Offset: 1

Views

Author

José María Grau Ribas, Feb 19 2012

Keywords

Comments

Contains 2 * terms t of A350777 such that (t-3)/phi(t) = 2. - Max Alekseyev, Oct 26 2023

Crossrefs

Cf. A000010, A207574, A202855, A203966, A350777.

Programs

  • Mathematica
    Select[Range[20000000], !PrimeQ[#/2] && Divisible[#+2, EulerPhi[#]+2]&]
  • PARI
    for(n=1,1e5,if((n+2)%(eulerphi(n)+2)==0&&(n%2||!isprime(n/2)), print1(n", "))) \\ Charles R Greathouse IV, Mar 02 2012

Extensions

a(4)-a(5) from Max Alekseyev, Nov 06 2023

A226104 Numbers n such that phi(n)+3 divides n+3.

Original entry on oeis.org

1, 30, 42, 66, 78, 102, 114, 138, 174, 186, 195, 222, 246, 258, 282, 318, 354, 366, 402, 426, 438, 474, 498, 534, 582, 606, 618, 642, 654, 678, 762, 786, 822, 834, 894, 906, 942, 978, 1002, 1038, 1074, 1086, 1146, 1158, 1182, 1194, 1266, 1338, 1362, 1374, 1398
Offset: 1

Views

Author

José María Grau Ribas, May 26 2013

Keywords

Links

Crossrefs

Cf. A000010 (Euler's totient function).
Cf. A207574 (numbers n such that phi(n)+2 divides n+2).
Cf. A202855 (numbers n such that phi(n)-1 divides n).
Cf. A203966 (numbers n such that phi(n) divides n+1).

Programs

  • Mathematica
    Select[Range[2000], IntegerQ[(# + 3)/(EulerPhi[#] + 3)] &]
  • PARI
    is(n)=(n+3)%(eulerphi(n)+3)==0 \\ Charles R Greathouse IV, Nov 13 2013
  • Python
    from sympy import totient as phi
def ok(n): return (n+3) % (phi(n)+3) == 0
print([m for m in range(1, 1400) if ok(m)]) # Michael S. Branicky, Jan 30 2021

A207667 Numbers n such that phi(n) divides n+2.

Original entry on oeis.org

1, 2, 4, 6, 10, 30, 70, 510, 2590, 131070, 3359230, 167247870, 8589934590, 13985925344264190
Offset: 1

Views

Author

José María Grau Ribas, Feb 19 2012

Keywords

Comments

Contains 2 * A203966 as a subsequence. - Max Alekseyev, Oct 27 2023

Crossrefs

Cf. A000010, A050474, A207574, A202855, A203966.

Programs

  • Mathematica
    Select[Range[50000000],Divisible[#+2,EulerPhi[#]]&]

Extensions

a(12)-a(13) from Donovan Johnson, Mar 01 2012
a(14) from Max Alekseyev, Oct 27 2023
Showing 1-3 of 3 results.

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

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