1,093 research outputs found
Permutations destroying arithmetic progressions in finite cyclic groups
A permutation \pi of an abelian group G is said to destroy arithmetic
progressions (APs) if, whenever (a,b,c) is a non-trivial 3-term AP in G, that
is c-b=b-a and a,b,c are not all equal, then (\pi(a),\pi(b),\pi(c)) is not an
AP. In a paper from 2004, the first author conjectured that such a permutation
exists of Z/nZ, for all n except 2,3,5 and 7. Here we prove, as a special case
of a more general result, that such a permutation exists for all n >= n_0, for
some explcitly constructed number n_0 \approx 1.4 x 10^{14}. We also construct
such a permutation of Z/pZ for all primes p > 3 such that p = 3 (mod 8).Comment: 11 pages, no figure
Crucial and bicrucial permutations with respect to arithmetic monotone patterns
A pattern is a permutation, and an arithmetic occurrence of in
(another) permutation is a subsequence
of that is order isomorphic to
where the numbers form an arithmetic progression. A
permutation is -crucial if it avoids arithmetically the patterns
and but its extension to the right by any element
does not avoid arithmetically these patterns. A -crucial permutation
that cannot be extended to the left without creating an arithmetic occurrence
of or is called -bicrucial.
In this paper we prove that arbitrary long -crucial and
-bicrucial permutations exist for any . Moreover, we
show that the minimal length of a -crucial permutation is
, while the minimal length of a
-bicrucial permutation is at most ,
again for
Van der Waerden's Theorem and Avoidability in Words
Pirillo and Varricchio, and independently, Halbeisen and Hungerbuhler
considered the following problem, open since 1994: Does there exist an infinite
word w over a finite subset of Z such that w contains no two consecutive blocks
of the same length and sum? We consider some variations on this problem in the
light of van der Waerden's theorem on arithmetic progressions.Comment: Co-author added; new result
- β¦