OFFSET
-3,4
COMMENTS
Series expansion of elliptical invariant for a cubic anharmonic group. Suggested by the anharmonic group elliptical invariant A078907.
If Y is a 4-subset of an n-set X then, for n>=7, a(n-3) is the number of 2-subsets of X which do not have exactly one element in common with Y. - Milan Janjic, Dec 28 2007
REFERENCES
McKean and Moll, Elliptic Curves, 1997, Cambridge University Press, page 20.
LINKS
FORMULA
a(n-7)=1/2*n^2-9/2*n+16, n=7,8,9,... - Milan Janjic, Dec 28 2007
MATHEMATICA
b = ReplacePart[Table[Coefficient[Series[(x^3 - x + 1)^3/(x^3*(1 - x)^3), {x, 0, 30}], x^n], {n, -3, 30}], 3, 4]
LinearRecurrence[{3, -3, 1}, {1, 0, 0, 3, 3, 3, 6, 9, 12, 16}, 60] (* Harvey P. Dale, Sep 29 2024 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Jan 29 2006
EXTENSIONS
Edited by N. J. A. Sloane, Apr 21 2007
STATUS
approved