OFFSET
1,2
FORMULA
Empirical: a(n) = (n^6 + 9*n^5 + 70*n^4 + 135*n^3 +64*n^2 -279*n +90)/90.
From G. C. Greubel, May 26 2016: (Start)
Empirical G.f.: x*(x^6 - 3*x^5 + x^4 + 16*x^3 - 27*x^2 +19*x +1)/(1-x)^7.
Empirical E.g.f.: (1/90)*(90 + 1125*x^2 + 870*x^3 + 225*x^4 + 24*x^5 + x^6)*exp(x) - 1. (End)
EXAMPLE
Some solutions for n=4
...1.1.1...1.1.2...1.2.2...1.1.3...1.1.1...1.1.1...1.2.2...1.1.3...1.2.3
...1.1.1...2.2.2...1.2.2...2.2.3...1.1.1...1.1.2...1.2.2...1.3.3...3.3.3
...1.1.3...2.3.2...3.3.3...2.2.3...1.1.3...2.2.2...2.2.2...2.2.3...3.3.3
...1.2.3...3.3.3...3.3.3...2.2.3...2.2.2...2.2.3...3.3.3...3.3.3...3.3.3
------
...1.3.3...1.1.1...1.1.1...1.1.3...1.1.1...1.1.2...1.2.2...1.1.2...1.1.3
...1.3.3...1.1.3...1.2.2...1.2.2...1.2.2...1.2.2...1.2.3...2.2.2...1.2.3
...2.2.3...1.2.3...1.2.3...2.2.2...2.2.3...1.2.2...2.2.2...2.2.2...1.3.3
...2.3.3...1.2.3...2.2.3...2.2.2...3.3.3...3.3.3...2.2.2...2.3.3...3.3.3
CROSSREFS
KEYWORD
nonn,more
AUTHOR
R. H. Hardin, Oct 21 2009
STATUS
approved