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 1-2 of 2 results.

A074964 Numbers k such that Max ( sigma(x*y) : 1 <= x <= k, 1 <= y <= k ) = sigma(k^2).

Original entry on oeis.org

1, 2, 3, 4, 6, 8, 12, 18, 24, 60
Offset: 1

Views

Author

Benoit Cloitre, Oct 05 2002

Keywords

Comments

Sequence is probably finite.
The next term in the sequence, if it exists, is larger than 40000. - Stewart Gordon, Sep 27 2011
Conjecture: subsequence of A066522, implying finiteness. - Reinhard Zumkeller, Nov 14 2011

Crossrefs

Cf. A000203, A066522, A065764, A074963.

Programs

  • Haskell
    a074964 n = a074964_list !! (n-1)
a074964_list = filter (\x -> a074963 x == a065764 x) [1..]
-- Reinhard Zumkeller, Nov 14 2011
  • Maple
    with(numtheory): s := proc(n) option remember: return sigma(n): end: a:= proc(n) option remember: if(n=0)then return 0: fi: return max(a(n-1),seq(s(x*n),x=1..n)): end: for n from 1 to 100 do if(a(n)=s(n^2))then printf("%d, ", n): end: od: # Nathaniel Johnston, Sep 26 2011
  • PARI
    isok(k) = vecmax(setbinop((x,y)->sigma(x*y), [1..k])) == sigma(k^2); \\ Michel Marcus, Feb 03 2022

Formula

A074963(a(n)) = A065764(a(n)). - Reinhard Zumkeller, Nov 14 2011

A127702 Least value of x*y giving Max ( sigma(x*y) : 1<=x<=n, 1<=y<=n ).

Original entry on oeis.org

1, 4, 9, 16, 20, 36, 42, 64, 72, 90, 90, 144, 144, 168, 210, 240, 240, 324, 324, 360, 420, 420, 420, 576, 600, 600, 600, 756, 756, 840, 840, 960, 960, 960, 960, 1260, 1260, 1260, 1260, 1560, 1560, 1680, 1680, 1680, 1980, 1980, 1980, 2160, 2160, 2400, 2400
Offset: 1

Views

Author

Stewart Gordon, Sep 26 2011

Keywords

Comments

Value is unique by this definition up to a(103) = 9900. To go beyond this number, we could define the sequence in terms of "smallest value of x*y" or "largest value of x*y". We choose smallest here.

Examples

			a(5) = 4 * 5 = 20; sigma(20) = 42

Crossrefs

Cf. A074963, A074964.
Showing 1-2 of 2 results.

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

Content is available under The OEIS End-User License Agreement.