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.

A068078 Numbers k such that (sigma(k)+sigma(k+1))/k is an integer.

Original entry on oeis.org

1, 10, 34, 136, 169, 2402, 5329, 21004, 38184, 41164, 54722, 458010, 776112, 1060802, 5026562, 10800112, 11108164, 14366402, 65676408, 87026656, 102944992, 387999360, 1488668112, 4414086384, 10499710072, 28645019964
Offset: 1

Views

Author

Dean Hickerson, Feb 16 2002

Keywords

Comments

The quotient (sigma(a(n))+sigma(a(n)+1))/a(n) is equal to 3 or 4 for n <= 33 and equal to 5 for a(34) = 1170035543040. - Giovanni Resta, Apr 04 2014

Links

Crossrefs

Cf. A067806, A068077.

Programs

  • Mathematica
    For[n=1, True, n++, If[Mod[DivisorSigma[1, n]+DivisorSigma[1, n+1], n]==0, Print[n]]]

Extensions

a(22)-a(26) from Donovan Johnson, Jan 31 2009

A068077 Numbers k such that sigma(k) + sigma(k+1) = 4k.

Original entry on oeis.org

1, 38184, 458010, 776112, 65676408, 1488668112, 4414086384, 28645019964, 46696401675, 65466785748, 70619381496, 176151711072
Offset: 1

Views

Author

Dean Hickerson, Feb 16 2002

Keywords

Comments

a(13) > 10^13. - Giovanni Resta, Jul 11 2013

Crossrefs

Cf. A000203 (sigma), A067806, A068078.

Programs

  • Mathematica
    For[n=1, True, n++, If[DivisorSigma[1, n]+DivisorSigma[1, n+1]==4n, Print[n]]]

Extensions

a(6)-a(8) from Donovan Johnson, Jan 31 2009
a(9)-a(12) from Giovanni Resta, Jul 11 2013

A222174 Numbers n such that sigma(n) + sigma(n-1) = 3n, where sigma(n) = sum of divisors of n (A000203).

Original entry on oeis.org

6, 34, 50, 236, 262, 386, 898, 8362, 26938, 46594, 80876, 5244548, 5462384, 17062316, 323987588, 1162300834, 1381439876
Offset: 1

Views

Author

Jaroslav Krizek, May 13 2013

Keywords

Comments

34 is the only number < 10^10 such that sigma(n) + sigma(n+1) = sigma(n) + sigma(n-1) = 3n (34 is a term of A067806).
a(16) > 5*10^8. - Giovanni Resta, May 13 2013
a(18) > 10^10. - Donovan Johnson, May 13 2013

Crossrefs

Cf. A067806 (numbers n such that sigma(n) + sigma(n+1) = 3n), A000203.

Programs

  • Mathematica
    For[n=1, True, n++, If[DivisorSigma[1, n]+DivisorSigma[1, n-1]==3n, Print[n]]]
  • PARI
    is(n)=sigma(n)+sigma(n-1)==3*n \\ Charles R Greathouse IV, May 13 2013

Extensions

a(12)-a(15) from Giovanni Resta, May 13 2013
a(16)-a(17) from Donovan Johnson, May 13 2013
Showing 1-3 of 3 results.

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

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