OFFSET
2,1
LINKS
R. H. Hardin, Table of n, a(n) for n=2..58
FORMULA
Empirical: a(n) = 12*a(n-1) - 63*a(n-2) + 190*a(n-3) - 363*a(n-4) + 456*a(n-5) - 377*a(n-6) + 198*a(n-7) - 60*a(n-8) + 8*a(n-9) for n>=13.
Conjectures from Colin Barker, Feb 26 2018: (Start)
G.f.: x^2*(3 + 4*x + 14*x^2 - 88*x^3 + 108*x^4 + 8*x^5 - 98*x^6 + 60*x^7 + 9*x^8 - 16*x^9 + 4*x^10) / ((1 - x)^6*(1 - 2*x)^3).
a(n) = (-314880 + 315315*2^n - (139264+79785*2^n)*n + 5*(-5248+1323*2^n)*n^2 - 3280*n^3 - 160*n^4 - 16*n^5) / 240 for n>3.
(End)
EXAMPLE
Some solutions for n=4:
...1.2.2.2.......1.1.2.2.......1.2.2.2.......1.1.3.2.......1.1.2.2....
.....2.2.2.3.......2.2.2.2.......4.4.4.4.......3.3.2.2.......3.3.2.4..
.......3.3.3.4.......3.2.2.4.......3.4.4.4.......3.3.4.4.......3.4.4.4
------
...1.1.1.2.......1.1.2.2.......1.1.1.2.......1.1.1.2.......1.1.2.2....
.....1.3.2.2.......1.3.2.4.......3.3.3.3.......1.3.2.4.......3.3.3.3..
.......3.2.2.4.......3.4.4.4.......3.3.3.4.......3.4.4.4.......3.3.3.4
------
...1.2.2.2.......1.1.3.2.......1.1.2.2.......1.1.1.2.......1.1.2.2....
.....3.3.3.3.......3.3.3.3.......1.1.1.1.......2.2.2.2.......1.3.2.4..
.......3.3.4.4.......3.3.4.4.......3.3.3.4.......3.2.2.4.......3.3.4.4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 17 2009
STATUS
approved