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 A208502 Number of 4 X n 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 1 0 and 1 1 1 vertically. 1
 9, 81, 126, 324, 828, 2124, 5436, 13932, 35676, 91404, 234108, 599724, 1536156, 3935052, 10079676, 25819884, 66138588, 169418124, 433972476, 1111644972, 2847534876, 7294114764, 18684254268, 47860713324, 122597730396, 314040583692 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Row 4 of A208501. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = a(n-1) + 4*a(n-2) for n>4. Conjectures from Colin Barker, Jul 03 2018: (Start) G.f.: 9*x*(1 + 8*x + x^2 - 14*x^3) / (1 - x - 4*x^2). a(n) = (9*2^(-6-n)*((1-sqrt(17))^n*(-109+27*sqrt(17)) + (1+sqrt(17))^n*(109+27*sqrt(17)))) / sqrt(17) for n>2. (End) EXAMPLE Some solutions for n=4: ..0..1..0..0....1..1..1..0....1..0..1..0....1..0..1..1....1..1..0..0 ..0..1..1..0....0..1..0..1....1..1..0..1....1..0..1..1....1..0..1..0 ..1..0..1..0....1..0..1..1....0..1..1..1....0..1..0..0....0..1..1..0 ..1..1..0..1....1..1..1..0....1..0..1..0....1..1..1..1....0..1..0..1 CROSSREFS Cf. A208501. Sequence in context: A209220 A207689 A209225 * A175370 A207695 A158028 Adjacent sequences: A208499 A208500 A208501 * A208503 A208504 A208505 KEYWORD nonn AUTHOR R. H. Hardin, Feb 27 2012 STATUS approved

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Last modified June 1 20:24 EDT 2023. Contains 363078 sequences. (Running on oeis4.)