English

Moments for generalizations of a coin flip game

Combinatorics 2026-05-20 v1 Probability

Abstract

We derive a recursive formula for the moments of the number of flips using a possibly biased coin to produce a prescribed finite binary string SS when SS is either a run of heads or a run of heads followed by a tails. Our recursive formula involve certain sums, which we simplify by using a one-parameter extension of the well-studied Eulerian number, which belongs to the two-parameter family of numbers introduced by Graham, Knuth, and Patashnik. We also use the Goulden--Jackson cluster method and Fa\`a di Bruno's formula to establish a closed formula for the moments in a more general situation where a die having an arbitrary number of faces with possibly different probabilities is rolled repeatedly until a prescribed finite word occurs.

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Cite

@article{arxiv.2605.19904,
  title  = {Moments for generalizations of a coin flip game},
  author = {Jia Huang},
  journal= {arXiv preprint arXiv:2605.19904},
  year   = {2026}
}

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12 pages