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 A227121 Number of n X 2 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 3 binary array having a sum of zero, with rows and columns of the latter in lexicographically nondecreasing order. 1
 3, 7, 13, 23, 40, 68, 112, 178, 273, 405, 583, 817, 1118, 1498, 1970, 2548, 3247, 4083, 5073, 6235, 7588, 9152, 10948, 12998, 15325, 17953, 20907, 24213, 27898, 31990, 36518, 41512, 47003, 53023, 59605, 66783, 74592, 83068, 92248, 102170, 112873 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = (1/24)*n^4 - (1/12)*n^3 + (11/24)*n^2 + (31/12)*n. Conjectures from Colin Barker, Sep 07 2018: (Start) G.f.: x*(3 - 8*x + 8*x^2 - 2*x^3) / (1 - x)^5. a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5. (End) EXAMPLE Some solutions for n=4: ..1..0....0..0....1..0....1..1....1..1....1..0....0..0....1..1....0..0....1..1 ..1..0....0..0....1..0....1..0....1..1....0..0....0..0....1..1....0..1....0..0 ..0..0....0..0....1..0....1..0....1..1....0..0....0..1....1..0....0..1....0..0 ..0..0....0..0....1..0....1..0....1..1....0..0....0..1....1..0....0..0....0..1 CROSSREFS Column 2 of A227125. Sequence in context: A122886 A154691 A306902 * A078447 A066624 A317783 Adjacent sequences:  A227118 A227119 A227120 * A227122 A227123 A227124 KEYWORD nonn AUTHOR R. H. Hardin, Jul 01 2013 STATUS approved

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Last modified January 20 23:16 EST 2020. Contains 331104 sequences. (Running on oeis4.)