Journal of Integer Sequences, Vol. 28 (2025), Article 25.4.1

Rigged Horse Numbers and their Modular Periodicity


Benjamin Schreyer
Departments of Computer Science and Physics
University of Maryland
College Park, MD 20742
USA
and
Plasma Physics Division
U.S. Naval Research Laboratory
Washington, D.C. 20375
USA

Abstract:

The Fubini numbers count the permutations of horse racing where ties are possible. The closely related r-horse numbers count the finishes of a horse race where some subset of r horses agree to finish the race in a specific relative strong ordering. We express the r-Fubini numbers as a sum of r index-shifted sequences of Fubini numbers weighted with the signed Stirling numbers of the first kind. We use a novel shift operator counting argument. Further, we demonstrate the eventual modular periodicity of r-Fubini numbers. Their maximum period is determined to be the Carmichael function of the modulus. The maximum period occurs in the case of an odd modulus for Fubini numbers.


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(Concerned with sequences A000670 A002322 A008275 A008277 A232473 A232474.)


Received August 2 2024; revised versions received August 3 2024; August 19 2024; November 27 2024; November 29 2024. Published in Journal of Integer Sequences, July 31 2025.


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