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 A218657 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 2 array. 2
 3, 15, 57, 225, 891, 3519, 13905, 54945, 217107, 857871, 3389769, 13394241, 52925643, 209128959, 826346529, 3265203393, 12902036643, 50980759695, 201443999193, 795980386593, 3145215436443, 12427919466687, 49107345869169 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Column 2 of A218663. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + 3*a(n-3). Empirical g.f.: 3*x*(1 + x)^2 / (1 - 3*x - 3*x^2 - 3*x^3). - Colin Barker, Mar 10 2018 EXAMPLE Some solutions for n=3: ..1..1....1..1....1..0....0..0....1..1....0..1....0..1....0..0....1..1....0..0 ..1..1....1..0....1..1....0..1....0..1....0..0....1..0....1..0....0..1....0..1 ..1..1....0..1....1..1....0..0....0..1....1..0....0..1....1..1....0..0....0..1 CROSSREFS Cf. A218663. Sequence in context: A118048 A210448 A284699 * A218804 A125673 A123007 Adjacent sequences:  A218654 A218655 A218656 * A218658 A218659 A218660 KEYWORD nonn AUTHOR R. H. Hardin, Nov 04 2012 STATUS approved

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Last modified May 31 00:53 EDT 2020. Contains 334747 sequences. (Running on oeis4.)