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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A015796 Numbers k such that phi(k) + 5 | sigma(k).

Original entry on oeis.org

4, 10, 32, 60, 88, 688, 2544, 3424, 12200, 62848, 777984, 1037824, 16734208, 67022848, 8625555968, 51537444864, 1099500617728
Offset: 1

Views

Author

Robert G. Wilson v

Keywords

Comments

a(18) <= 17592142004224. In general, if 2^k-11 is prime (A096817) then 2^(k-2)*3*(2^k-11) is a term for k > 3. Moreover, if 2^k-21 is prime (A096820) then 2^(k-2)*(2^k-21) is a term for k > 4. - Giovanni Resta, Sep 09 2019

Crossrefs

Cf. A000010, A000203, A056097, A015812, A015792, A015793, A015797, A015798, A015799, A015800, A015801, A015804, A015805, A096817, A096820.

Programs

  • Mathematica
    Select[Range[100000],
Divisible[DivisorSigma[1, #], EulerPhi[#] + 5] &] (* David Nacin, Feb 28 2012 *)

Extensions

More terms from Jud McCranie, Dec 26 1999
Offset corrected and a(15)-a(16) from Donovan Johnson, Feb 28 2012
a(17) from Giovanni Resta, Sep 09 2019
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