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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
OFFSET
1,2
LINKS
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 01 2010
STATUS
approved