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 A326499 a(n) = A046693(n) - A309407(n). Excess E of a length n sparse ruler. 3
 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 50,0 COMMENTS Excess = minimal length n sparse ruler marks - round(sqrt(3*n + 9/4)). The first fifty terms are 0. A308766 lists n values with excess 1. Luschny's conjecture: 1^3 24^1 5^1 4^5 3^2 with length 58 is the last non-Wichmann optimal ruler. If this is true, all terms are 0 or 1. Taking terms in batches based on A289761 leads to pattern illustrated at A046693. Terms over n = 213 are unverified minimal. "Dark Satanic Mills on a Cloudy Day." - N. J. A. Sloane This is a hard sequence due to minimality verification. For example, n=474 has E=1, but it's possible an E=0 sparse ruler exists. LINKS J. Leech, On the representation of 1, 2, ..., n by differences, J. Lond. Math. Soc. 31 (1956), 160-169. Peter Luschny, Perfect and Optimal Rulers Peter Luschny, Are optimal rulers of Wichmann type? Peter Luschny, Perfect Rulers. Peter Luschny, Wichmann Rulers. Ed Pegg Jr., Sparse Rulers (Wolfram Demonstrations Project) Ed Pegg Jr., Wichmann-like Rulers (Wolfram Demonstrations Project) Ed Pegg Jr, Table of n, a(n) for n=1..10501 in batches of A289761. Transpose for Dark Mills pattern. Ed Pegg Jr, Picture of a(n) for n = 1..10501 in batches of A289761. This is the Dark Mills pattern. L. Rédei, A. Rényi, On the representation of the numbers 1, 2, ..., N by means of differences, Matematicheskii Sbornik, Vol. 24(66) Num. 3 (1949), 385-389 (in Russian). Arch D. Robison, Parallel Computation of Sparse Rulers, Jan 14 2014. B. Wichmann, A note on restricted difference bases, J. Lond. Math. Soc. 38 (1963), 465-466. EXAMPLE 0, 1, 2, 3, 4, 10, 16, 22, 28, 34, 40, 46, 51 is a sparse ruler of length 51 with 13 marks, the fewest possible. 13 - round(sqrt(3*51+9/4)) = 13 - 12 = 1. CROSSREFS Cf. A046693, A289761, A308766, A309407. Sequence in context: A126811 A014057 A015689 * A104124 A052434 A015241 Adjacent sequences:  A326496 A326497 A326498 * A326500 A326501 A326502 KEYWORD nonn,hard AUTHOR Ed Pegg Jr, Sep 12 2019 EXTENSIONS E<=1 proved by Ed Pegg Jr, Oct 16 2019 STATUS approved

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Last modified January 23 22:16 EST 2020. Contains 331177 sequences. (Running on oeis4.)