Nonexistence of almost Moore digraphs of degrees 4 and 5 with self-repeats

An almost Moore (d,k)-digraph is a regular digraph of degree d>1, diameter k>1 and order N(d,k)=d+d2+⋯+dk. So far, their existence has only been shown for k=2, whilst it is known that there are no such digraphs for k=3, 4 and for d=2, 3 when k≥3. Furthermore, under certain assumptions, the nonexistence for the remaining cases has also been shown. In this paper, we prove that (4,k) and (5,k)-almost Moore digraphs with self-repeats do not exist for k≥5.Nacho López: Supported in part by grants PID2020-115442RB-I00 and 2021 SGR-00434. Arnau Messegué: Supported in part by grants Margarita Sala and 2021SGR-00434. Josep M. Miret: Supported in part by grants PID2021-124613OB-I00 and 2021 SGR-00434.Peer ReviewedPostprint (published version

Nonexistence of almost Moore digraphs of diameter four

Regular digraphs of degree d > 1, diameter k > 1 and order N(d; k) = d+ +dk will be called almost Moore (d; k)-digraphs. So far, the problem of their existence has only been solved when d = 2; 3 or k = 2; 3. In this paper we prove that almost Moore digraphs of diameter 4 do not exist for any degree dPostprint (published version

On the nonexistence of almost Moore digraphs

Digraphs of maximum out-degree at most d > 1, diameter at most k > 1 and order N(d, k) = d + ... + d(k) are called almost Moore or (d, k)-digraphs. So far, the problem of their existence has been solved only when d = 2, 3 or k = 2, 3, 4. In this paper we derive the nonexistence of (d, k)-digraphs, with k > 4 and d > 3, under the assumption of a conjecture related to the factorization of the polynomials Phi(n)(1 + x + ... + x(k)), where Phi(n)(x) denotes the nth cyclotomic polynomial and 1 < n <= N(d, k). Moreover, we prove that almost Moore digraphs do not exist for the particular cases when k = 5 and d = 4, 5 or 6. (C) 2014 Elsevier Ltd. All rights reserved.Postprint (published version

On the nonexistence of almost Moore digraphs

Digraphs of maximum out-degree at most d > 1, diameter at most k > 1 and order N(d, k) = d + ... + d(k) are called almost Moore or (d, k)-digraphs. So far, the problem of their existence has been solved only when d = 2, 3 or k = 2, 3, 4. In this paper we derive the nonexistence of (d, k)-digraphs, with k > 4 and d > 3, under the assumption of a conjecture related to the factorization of the polynomials Phi(n)(1 + x + ... + x(k)), where Phi(n)(x) denotes the nth cyclotomic polynomial and 1 < n <= N(d, k). Moreover, we prove that almost Moore digraphs do not exist for the particular cases when k = 5 and d = 4, 5 or 6. (C) 2014 Elsevier Ltd. All rights reserved

Nonexistence of almost Moore digraphs of diameter four

Regular digraphs of degree d > 1, diameter k > 1 and order N(d; k) = d+ +dk will be called almost Moore (d; k)-digraphs. So far, the problem of their existence has only been solved when d = 2; 3 or k = 2; 3. In this paper we prove that almost Moore digraphs of diameter 4 do not exist for any degree