OFFSET
1,3
FORMULA
Complicated linear recurrence in terms of 4 variables known.
Empirical g.f.: -x^3*(2*x^8 + 4*x^5 + 4*x^4 + 3*x^3 + 3*x^2 + 5*x + 2) / (2*x^10 + 4*x^7 + 3*x^6 + x^5 + 2*x^4 + 3*x^3 - 1). [Colin Barker, Nov 29 2012]
EXAMPLE
a(5)=3 because of the tilings
aaabb aabbb abbbc
ccddd cccdd adddc
CROSSREFS
KEYWORD
nonn
AUTHOR
I seem to have no record of the source for this sequence. - N. J. A. Sloane
STATUS
approved