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 A218806 Hilltop maps: number of n X 4 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..3 n X 4 array. 1
 15, 249, 3969, 63499, 1015887, 16252713, 260019585, 4159932363, 66552822351, 1064747639097, 17034402072321, 272525472991467, 4360008241786383, 69753743236473129, 1115957683030959873, 17853687738218017899 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Column 4 of A218810. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 15*a(n-1) + 15*a(n-2) + 15*a(n-3) + 9*a(n-4) + 9*a(n-5) + 9*a(n-6) + 9*a(n-7). Empirical g.f.: x*(15 + 24*x + 9*x^2 + 4*x^3 - 3*x^4 + 12*x^5 + 3*x^6) / (1 - 15*x - 15*x^2 - 15*x^3 - 9*x^4 - 9*x^5 - 9*x^6 - 9*x^7). - Colin Barker, Jul 24 2018 EXAMPLE Some solutions for n=3: ..0..0..1..0....1..0..1..0....1..0..1..0....1..0..0..0....1..0..1..0 ..1..1..1..0....1..0..1..0....0..0..0..1....1..0..1..1....0..1..1..0 ..1..0..0..0....1..0..0..0....0..1..1..1....0..1..1..0....1..1..1..0 CROSSREFS Cf. A218810. Sequence in context: A065920 A273624 A223424 * A285395 A331493 A093147 Adjacent sequences:  A218803 A218804 A218805 * A218807 A218808 A218809 KEYWORD nonn AUTHOR R. H. Hardin, Nov 06 2012 STATUS approved

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Last modified June 6 11:14 EDT 2020. Contains 334827 sequences. (Running on oeis4.)