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 A180374 1/120 the number of n X 3 arrays of integers in 1..6 with no element or any of its neighbors having the same value. 1
 1, 21, 156, 1236, 9552, 74568, 579792, 4515312, 35141952, 273573984, 2129509056, 16576843584, 129037857024, 1004466036864, 7819018652928, 60865289156352, 473791157511168, 3688113552987648, 28709232900123648, 223480124314162176 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS R. H. Hardin, Table of n, a(n) for n=1..99 FORMULA Empirical (for n>=5): a(n) = 6*a(n-1) + 18*a(n-2) - 32*a(n-3). - Vaclav Kotesovec, Nov 27 2012 Empirical g.f.: x*(1 + 15*x + 12*x^2 - 46*x^3) / (1 - 6*x - 18*x^2 + 32*x^3). - Colin Barker, Mar 26 2018 CROSSREFS Sequence in context: A301883 A302080 A331528 * A108675 A296832 A267473 Adjacent sequences:  A180371 A180372 A180373 * A180375 A180376 A180377 KEYWORD nonn AUTHOR R. H. Hardin, Sep 01 2010 STATUS approved

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Last modified January 26 14:08 EST 2020. Contains 331280 sequences. (Running on oeis4.)