## Abstract

Let k≤n be two positive integers, and let F be a field with characteristic p. A sequence f : {1,...,n} → F is called k-constant, if the sum of the values of f is the same for every arithmetic progression of length k in {1,...,n}. Let V(n, k, F) be the vector space of all k-constant sequences. The constant sequence is, trivially, k-constant, and thus dim V(n, k, F)≥1. Let m(k, F)= min^{∞}_{n=k} dim V(n, k, F), and let c(k, F) be the smallest value of n for which dim V(n, k, F)=m(k, F). We compute m(k, F) for all k and F and show that the value only depends on k and p and not on the actual field. In particular, we show that if p#2224;k (in particular, if p = 0) then m(k, F) = 1 (namely, when n is large enough, only constant functions are k constant). Otherwise, if k = p^{r}t where r ≥ 1 is maximal, then m(k, F) = k - t. We also conjecture that c(k, F) = (k - 1)t + φ(t), unless p > t and p divides k, in which case c(k, F) = (k - 1)p + 1 (in case p#2224;A: we put t = k), where φ(t) is Euler's function. We prove this conjecture in case t is a multiple of at most two distinct prime powers. Thus, in particular, we get that whenever k = q^{s1}_{1} q^{s2}_{2} where q_{1}, q_{2} are distinct primes and p ≠ q_{1}, q_{2}, then every k-constant sequence is constant if and only if n≥q^{2s1}_{1} q^{2s2}_{2} - q^{s1-1}_{1} q^{s2-1}_{2}(q_{1} + q_{2} - 1). Finally, we establish an interesting connection between the conjecture regarding c(k, F) and a conjecture about the non-singularity of a certain (0, 1)-matrix over the integers.

Original language | English |
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Pages (from-to) | 225-237 |

Number of pages | 13 |

Journal | Discrete Mathematics |

Volume | 224 |

Issue number | 1-3 |

DOIs | |

State | Published - 28 Sep 2000 |

## ASJC Scopus subject areas

- Theoretical Computer Science
- Discrete Mathematics and Combinatorics