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47
Higher correlations of divisor sums related to primes, II: Variations of . . .
, 2007
"... We calculate the triple correlations for the truncated divisor sum λR(n). The λR(n) behave over certain averages just as the prime counting von Mangoldt function Λ(n) does or is conjectured to do. We also calculate the mixed (with a factor of Λ(n)) correlations. The results for the moments up to the ..."
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We calculate the triple correlations for the truncated divisor sum λR(n). The λR(n) behave over certain averages just as the prime counting von Mangoldt function Λ(n) does or is conjectured to do. We also calculate the mixed (with a factor of Λ(n)) correlations. The results for the moments up to the third degree, and therefore the implications for the distribution of primes in short intervals, are the same as those we obtained (in the first paper with this title) by using the simpler approximation ΛR(n). However, when λR(n) is used, the error in the singular series approximation is often much smaller than what ΛR(n) allows. Assuming the Generalized Riemann Hypothesis (GRH) for Dirichlet Lfunctions, we obtain an Ω±result for the variation of the error term in the prime number theorem. Formerly, our knowledge under GRH was restricted to Ωresults for the absolute value of this variation. An important ingredient in the last part of this work is a recent result due to Montgomery and Soundararajan which makes it possible for us to dispense with a large error term in the evaluation of a certain singular series average. We believe that our results on the sums λR(n) and ΛR(n) can be employed in diverse problems concerning primes.
Moore graphs and beyond: A survey of the degree/diameter problem
 ELECTRONIC JOURNAL OF COMBINATORICS
, 2013
"... The degree/diameter problem is to determine the largest graphs or digraphs of given maximum degree and given diameter. General upper bounds – called Moore bounds – for the order of such graphs and digraphs are attainable only for certain special graphs and digraphs. Finding better (tighter) upper bo ..."
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Cited by 30 (4 self)
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The degree/diameter problem is to determine the largest graphs or digraphs of given maximum degree and given diameter. General upper bounds – called Moore bounds – for the order of such graphs and digraphs are attainable only for certain special graphs and digraphs. Finding better (tighter) upper bounds for the maximum possible number of vertices, given the other two parameters, and thus attacking the degree/diameter problem ‘from above’, remains a largely unexplored area. Constructions producing large graphs and digraphs of given degree and diameter represent a way of attacking the degree/diameter problem ‘from below’. This survey aims to give an overview of the current stateoftheart of the degree/diameter problem. We focus mainly on the above two streams of research. However, we could not resist mentioning also results on various related problems. These include considering Moorelike bounds for special types of graphs and digraphs, such as vertextransitive, Cayley, planar, bipartite, and many others, on
The Shannon Capacity of a union
 Combinatorica
, 1998
"... For an undirected graph G = (V; E), let G n denote the graph whose vertex set is V n in which two distinct vertices (u 1 ; u 2 ; : : : ; un ) and (v 1 ; v 2 ; : : : ; v n ) are adjacent iff for all i between 1 and n either u i = v i or u i v i 2 E. The Shannon capacity c(G) of G is the limit li ..."
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Cited by 25 (0 self)
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For an undirected graph G = (V; E), let G n denote the graph whose vertex set is V n in which two distinct vertices (u 1 ; u 2 ; : : : ; un ) and (v 1 ; v 2 ; : : : ; v n ) are adjacent iff for all i between 1 and n either u i = v i or u i v i 2 E. The Shannon capacity c(G) of G is the limit limn7!1 (ff(G n )) 1=n , where ff(G n ) is the maximum size of an independent set of vertices in G n . We show that there are graphs G and H such that the Shannon capacity of their disjoint union is (much) bigger than the sum of their capacities. This disproves a conjecture of Shannon raised in 1956. 1 Introduction For an undirected graph G = (V; E), let G n denote the graph whose vertex set is V n in which two distinct vertices (u 1 ; u 2 ; : : : ; u n ) and (v 1 ; v 2 ; : : : ; v n ) are adjacent iff for all i between 1 and n either u i = v i or u i v i 2 E. The Shannon capacity c(G) of G is the limit lim n7!1 (ff(G n )) 1=n , where ff(G n ) is the maximum size of an inde...
A Note on Large Graphs of Diameter Two and Given Maximum Degree
"... Let vt(d; 2) be the largest order of a vertextransitive graph of degree d and diameter two. It is known that vt(d; 2) = d 2 + 1 for d = 1; 2; 3, and 7; for the remaining values of d we have vt(d; 2) d 2 \Gamma 1. The only known general lower bound on vt(d; 2), valid for all d, seems to be vt(d ..."
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Cited by 19 (5 self)
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Let vt(d; 2) be the largest order of a vertextransitive graph of degree d and diameter two. It is known that vt(d; 2) = d 2 + 1 for d = 1; 2; 3, and 7; for the remaining values of d we have vt(d; 2) d 2 \Gamma 1. The only known general lower bound on vt(d; 2), valid for all d, seems to be vt(d; 2) b d+2 2 cd d+2 2 e. Using voltage graphs, we construct a family of vertextransitive nonCayley graphs which shows that vt(d; 2) 8 9 (d + 1 2 ) 2 for all d of the form d = (3q \Gamma 1)=2 where q is a prime power congruent with 1 (mod 4). The construction generalizes to all prime powers and yields large highly symmetric graphs for other degrees as well. In particular, for d = 7 we obtain as a special case the HoffmanSingleton graph, and for d = 11 and d = 13 we have new largest graphs of diameter two and degree d on 98 and 162 vertices, respectively. 1 Introduction The wellknown degree/diameter problem asks for determining the largest possible number n(d; k) of vertic...
Small gaps between prime numbers: the work of GoldstonPintzYıldırım
, 2000
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Small gaps between primes
"... ABSTRACT. We use short divisor sums to approximate prime tuples and moments for primes in short intervals. By connecting these results to classical moment problems we are able to prove that, for any η> 0, a positive proportion of consecutive primes are within 1 + η times the average spacing betwe ..."
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Cited by 10 (3 self)
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ABSTRACT. We use short divisor sums to approximate prime tuples and moments for primes in short intervals. By connecting these results to classical moment problems we are able to prove that, for any η> 0, a positive proportion of consecutive primes are within 1 + η times the average spacing between primes. 4 1.
On the irreducibility of a certain class of Laguerre polynomials
 J. Number Theory
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Primes in Tuples I
"... We introduce a method for showing that there exist prime numbers which are very close together. The method depends on the level of distribution of primes in arithmetic progressions. Assuming the ElliottHalberstam conjecture, we prove that there are infinitely often primes differing by 16 or less. E ..."
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Cited by 6 (1 self)
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We introduce a method for showing that there exist prime numbers which are very close together. The method depends on the level of distribution of primes in arithmetic progressions. Assuming the ElliottHalberstam conjecture, we prove that there are infinitely often primes differing by 16 or less. Even a much weaker conjecture implies that there are infinitely often primes a bounded distance apart. Unconditionally, we prove that there exist consecutive primes which are closer than any arbitrarily small multiple of the average spacing, that is, pn+1 − pn lim inf =0. n→ ∞ log pn We will quantify this result further in a later paper (see (1.9) below).
A Trace Bound for the Hereditary Discrepancy
, 2001
"... Let A be the incidence matrix of a set system with m sets and n points, m ≤ n, and let t = tr M, where M = AT A. Finally, let σ = tr M 2 be the sum of squares of the elements of M. We prove that the hereditary discrepancy of the set system is at least 1 4 cnσ/t2√ 1 t/n, with c =. This general trac ..."
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Cited by 5 (2 self)
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Let A be the incidence matrix of a set system with m sets and n points, m ≤ n, and let t = tr M, where M = AT A. Finally, let σ = tr M 2 be the sum of squares of the elements of M. We prove that the hereditary discrepancy of the set system is at least 1 4 cnσ/t2√ 1 t/n, with c =. This general trace bound allows us to resolve discrepancytype 324 questions for which spectral methods had previously failed. Also, by using this result in conjunction with the spectral lemma for linear circuits, we derive new complexity bounds for range searching. • We show that the (red–blue) discrepancy of the set system formed by n points and n lines in the plane is �(n1/6) in the worst case and always1 Õ(n1/6). • We give a simple explicit construction of n points and n halfplanes with hereditary discrepancy ˜�(n1/4). • We show that in any dimension d = �(log n/log log n), there is a set system of n points and n axisparallel boxes in Rd with discrepancy n�(1/log log n). • Applying these discrepancy results together with a new variation of the spectral lemma, we derive a lower bound of �(n log n) on the arithmetic complexity of offline range searching for points and lines (for nonmonotone circuits). We also prove a lower bound of �(n log n/log log n) on the complexity of orthogonal range searching in any dimension �(log n/log log n).