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 A005047 Minimal span of set of n elements with no 3-term arithmetic progression. 10
 0, 1, 3, 4, 8, 10, 12, 13, 19, 23, 25, 29, 31, 35, 39, 40, 50, 53, 57, 62, 70, 73, 81, 83, 91, 94, 99, 103, 110, 113, 120, 121, 136, 144, 149, 156, 162, 164, 168, 173, 193, 203, 208 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Length of shortest ruler with n marks, with no mark halfway between two other marks. - Christian Häggström, Nov 19 2018 REFERENCES R. K. Guy, Unsolved Problems in Number Theory, E10 (but beware of errors). LINKS B. E. Brown and D. M. Gordon, On sequences without geometric progressions, Math. Comp. 65 (1996), no. 216, 1749-1754. FORMULA a(n) = A065825(n) - 1. EXAMPLE Example for a(10) = 23: 0 1 4 6 10 15 17 18 22 23. CROSSREFS Cf. A065825. Sequence in context: A191193 A047343 A155730 * A083317 A268514 A024514 Adjacent sequences:  A005044 A005045 A005046 * A005048 A005049 A005050 KEYWORD nonn,more AUTHOR EXTENSIONS a(18)-a(41) derived from A065825 by Rob Pratt, Jul 09 2015 a(1)-a(2) prepended and a(42)-a(43) derived from A065825 by Alois P. Heinz, Nov 18 2018 STATUS approved

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Last modified January 21 02:59 EST 2019. Contains 319344 sequences. (Running on oeis4.)