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A165392
Number of slanted 2 X n (i=1..2) X (j=i..n+i-1) 1..4 arrays with all 1s connected, all 2s connected, all 3s connected, all 4s connected, 1 in the upper left corner, 2 in the upper right corner, 3 in the lower left corner, 4 in the lower right corner, and with no element having more than 2 neighbors with the same value.
2
1, 9, 33, 65, 101, 146, 199, 260, 329, 406, 491, 584, 685, 794, 911, 1036, 1169, 1310, 1459, 1616, 1781, 1954, 2135, 2324, 2521, 2726, 2939, 3160, 3389, 3626, 3871, 4124, 4385, 4654, 4931, 5216, 5509, 5810, 6119, 6436, 6761, 7094, 7435, 7784, 8141, 8506
OFFSET
2,2
COMMENTS
Same recurrence for A165381.
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>=9.
Conjectures from Colin Barker, Feb 26 2018: (Start)
G.f.: x^2*(1 + 6*x + 9*x^2 - 8*x^3 - 4*x^4 + 5*x^5 - x^6) / (1 - x)^3.
a(n) = 4*n^2 - 7*n - 1 for n>5.
(End)
EXAMPLE
Some solutions for n=9:
...1.1.1.1.1.2.2.2.2.....1.1.1.1.1.1.2.2.2.....1.1.1.1.1.2.2.2.2..
.....3.3.3.1.1.1.1.2.4.....3.3.3.2.2.2.4.4.4.....3.3.3.1.1.4.4.4.4
------
...1.1.1.1.1.1.2.2.2.....1.3.3.3.3.3.3.2.2.....1.1.1.2.2.2.2.2.2..
.....3.3.3.3.4.4.4.4.4.....3.4.4.4.4.4.4.4.4.....3.3.3.3.3.4.4.4.4
------
...1.1.1.1.1.2.2.2.2.....1.1.1.1.1.1.1.1.2.....1.1.1.1.1.1.3.2.2..
.....3.3.3.2.2.4.4.4.4.....3.3.3.3.3.3.1.2.4.....3.3.3.3.3.3.2.2.4
CROSSREFS
Cf. A165381.
Sequence in context: A161430 A175369 A046895 * A145923 A092562 A103602
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved