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 A207864 Number of n X 2 nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to any horizontal or vertical neighbor (colorings ignoring permutations of colors). 3
 1, 4, 34, 500, 10900, 322768, 12297768, 580849872, 33093252880, 2227152575552, 174131286983712, 15604440074084672, 1584856558077903168, 180712593036822482176, 22946861101272125055616, 3222156375409363475703040 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS R. H. Hardin, Table of n, a(n) for n = 1..61 FORMULA It appears that the sequence terms are given by the Dobinski-type formula a(n+1) = 1/e * Sum_{k>=0} (1+k+k^2)^n/k!. - Peter Bala, Mar 12 2012 EXAMPLE Some solutions for n=5 ..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1 ..1..0....1..0....1..2....1..2....1..0....1..0....1..2....1..0....1..0....1..0 ..0..1....0..1....0..1....0..1....2..1....0..1....0..1....0..2....2..1....0..1 ..1..2....1..0....1..0....1..3....3..0....2..0....3..2....2..1....1..0....1..2 ..0..1....0..1....2..1....2..4....1..2....0..1....0..1....0..2....0..1....2..0 CROSSREFS Column 2 of A207868. Sequence in context: A002105 A198717 A198908 * A222077 A081972 A158961 Adjacent sequences:  A207861 A207862 A207863 * A207865 A207866 A207867 KEYWORD nonn AUTHOR R. H. Hardin Feb 21 2012 STATUS approved

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Last modified October 21 14:57 EDT 2018. Contains 316424 sequences. (Running on oeis4.)