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.

A289684 Mixing moments for the waiting time in an M/G/1 waiting queue.

Original entry on oeis.org

1, 2, 9, 42, 199, 950, 4554, 21884, 105323, 507398, 2446022, 11796884, 56912838, 274630876, 1325431956, 6397576888, 30882340531, 149084312006, 719736965358, 3474807470756, 16776410481266, 80998307687668, 391074406408716, 1888199373821896, 9116752061308798
Offset: 0

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Author

R. J. Mathar, Jul 09 2017

Keywords

Comments

In the preprint and the paper by Karpov et al., a(n) (resp. 2*a(n)) is the size of the Condorcet domain on 2*n (resp. 2*n+1) alternatives defined by the so-called even 1N33N1 scheme, cf. A144685. - Andrey Zabolotskiy, Jan 27 2024

Crossrefs

Programs

  • Maple
    f:= gfun:-rectoproc({n*a(n) +2*(-4*n+3)*a(n-1) +12*(n-2)*a(n-2) +8*(2*n-3)*a(n-3),a(0)=1,a(1)=2,a(2)=9,a(3)=42},a(n),remember):
    map(f, [$0..50]); # Robert Israel, Mar 31 2019
  • Mathematica
    CoefficientList[2 x^2/(4 x^2 + 2x + Sqrt[1 - 4x] - 1) + O[x]^25, x] (* Jean-François Alcover, Aug 26 2022 *)
  • Sage
    (2*x^2/(4*x^2+2*x+sqrt(1-4*x)-1)).series(x, 25).coefficients(x, sparse=False) # Stefano Spezia, Mar 19 2025

Formula

G.f.: 1/(2-A000108(x)^2), where A000108(x) is the generating function of the Catalan Numbers.
Conjecture: n*a(n) + 2*(-4*n+3)*a(n-1) + 12*(n-2)*a(n-2) + 8*(2*n-3)*a(n-3) = 0.
From Robert Israel, Mar 31 2019: (Start)
Conjecture verified (for n >= 4) using the differential equation (16*x^3 + 12*x^2 - 8*x + 1)*y' + (24*x^2 - 2)*y -12*x^2 + 2*x = 0 satisfied by the g.f.
a(n) ~ (sqrt(2)/4)*(2 + 2*sqrt(2))^n. (End)

A369614 Maximal size of Condorcet domain on n alternatives.

Original entry on oeis.org

1, 1, 2, 4, 9, 20, 45, 100, 224
Offset: 0

Views

Author

Andrey Zabolotskiy, Jan 27 2024

Keywords

Comments

A Condorcet domain is a set D of permutations of [n] such that for any i, j, k from [n] there do not exist three permutations in D in which i, j, k are ordered in all three different cyclic permutations of the order (i, j, k). If these permutations are interpreted as voters' preferences, this condition prevents the Condorcet effect.
Condorcet domains are also known as acyclic domains, acyclic sets of linear orders, consistent profiles, or consistent sets.

Examples

			For n <= 2, the set of all n! permutations is a Condorcet domain.
For n = 3, an example of a Condorcet domain of maximal size is the following set of permutations:
  123
  213
  231
  321
For n = 4, an example of a Condorcet domain of maximal size is:
  1234
  1324
  1342
  3124
  3142
  3412
  3421
  4312
  4321
		

Crossrefs

Cf. A144685 (size of Fishburn's alternating domain), A144686 (maximal size of Condorcet domain containing a maximal chain), A144687, A289684.

A144686 Maximal size of a connected acyclic domain of permutations of n elements with diameter n*(n-1)/2.

Original entry on oeis.org

1, 2, 4, 9, 20, 45, 100
Offset: 1

Views

Author

N. J. A. Sloane, Feb 07 2009

Keywords

Comments

a(n) is at most 2.487^n and at least 2.076^n for large enough n (see Felsner & Valtr). Originally conjectured to equal A144685, but in fact a(n) is asymptotically larger and exceeds A144685 at least for n >= 34 (see Karpov & Slinko). - Clayton Thomas, Aug 19 2019 [Updated by Andrey Zabolotskiy, Dec 31 2023]

References

  • B. Monjardet, Acyclic domains of linear orders: a survey, in "The Mathematics of Preference, Choice and Order: Essays in Honor of Peter Fishburn", edited by Steven Brams, William V. Gehrlein and Fred S. Roberts, Springer, 2009, pp. 139-160.

Crossrefs

Cf. A090245 (has same initial terms but probably is unrelated), A144685, A144687, A369614.

Extensions

a(1)-a(2) added and name edited by Andrey Zabolotskiy, Dec 31 2023
Showing 1-3 of 3 results.