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 A230929 Number of black-square subarrays of (n+2) X (2+2) 0..3 arrays x(i,j) with each element diagonally or antidiagonally next to at least one element with value (x(i,j)+1) mod 4, no adjacent elements equal, and upper left element zero. 2
 2, 6, 16, 48, 146, 438, 1312, 3936, 11810, 35430, 106288, 318864, 956594, 2869782, 8609344, 25828032, 77484098, 232452294, 697356880, 2092070640, 6276211922, 18828635766, 56485907296, 169457721888, 508373165666, 1525119496998 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Column 2 of A230935. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 3*a(n-1) - a(n-2) + 3*a(n-3). Empirical g.f.: 2*x / ((1 - 3*x)*(1 + x^2)). - Colin Barker, Mar 17 2018 EXAMPLE Some solutions for n=4: ..x..0..x..2....x..0..x..0....x..0..x..2....x..0..x..2....x..0..x..0 ..1..x..3..x....3..x..1..x....1..x..3..x....1..x..3..x....1..x..1..x ..x..2..x..2....x..2..x..3....x..2..x..0....x..2..x..2....x..2..x..2 ..1..x..3..x....0..x..0..x....3..x..1..x....3..x..3..x....3..x..3..x ..x..0..x..2....x..1..x..3....x..0..x..0....x..0..x..2....x..0..x..2 ..3..x..1..x....0..x..2..x....3..x..3..x....3..x..1..x....3..x..1..x CROSSREFS Cf. A230935. Sequence in context: A225178 A129772 A046721 * A291189 A214843 A272411 Adjacent sequences:  A230926 A230927 A230928 * A230930 A230931 A230932 KEYWORD nonn AUTHOR R. H. Hardin, Nov 01 2013 STATUS approved

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Last modified September 25 16:45 EDT 2020. Contains 337344 sequences. (Running on oeis4.)