OFFSET
2,1
LINKS
R. H. Hardin, Table of n, a(n) for n=2..41
FORMULA
Empirical: a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6) for n>=13.
Empirical g.f.: x^2*(105 + 1382*x + 6097*x^2 + 14754*x^3 + 21137*x^4 + 18104*x^5 + 9321*x^6 + 2666*x^7 + 218*x^8 - 58*x^9 + 2*x^10) / ((1 - x)^3*(1 + x)^3). - Colin Barker, Mar 26 2018
EXAMPLE
Some solutions for n=3:
...1.2.2.2.2.......1.2.2.2.2.......1.1.1.2.2.......1.1.1.2.2....
.....3.3.2.3.3.......2.3.2.4.4.......3.3.3.3.4.......3.3.2.4.4..
.......3.3.3.3.4.......3.3.3.4.4.......3.3.3.4.4.......3.3.3.4.4
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...1.1.2.2.2.......1.1.3.3.2.......1.1.1.1.2.......1.1.2.2.2....
.....3.3.2.2.2.......1.3.3.2.2.......2.2.2.2.4.......3.3.4.4.4..
.......3.3.3.3.4.......3.3.2.4.4.......3.2.4.4.4.......3.3.3.4.4
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...1.1.1.1.2.......1.1.1.1.2.......1.2.2.2.2.......1.1.3.3.2....
.....1.2.2.2.2.......3.3.3.2.2.......3.3.3.2.2.......3.3.2.2.3..
.......3.3.4.4.4.......3.3.4.4.4.......3.2.2.2.4.......3.3.3.3.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved