%I
%S 1,0,0,3,3,3,6,9,12,16,21,27,34,42,51,61,72,84,97,111,126,142,159,177,
%T 196,216,237,259,282,306,331,357,384,412,441,471,502,534,567,601,636,
%U 672,709,747,786,826,867,909,952,996,1041,1087,1134,1182,1231,1281,1332,1384,1437
%N G.f.: (x^3  x + 1)^3/(x^3*(1  x)^3).
%C Series expansion of elliptical invariant for a cubic anharmonic group. Suggested by the anharmonic group elliptical invariant A078907.
%C If Y is a 4subset of an nset X then, for n>=7, a(n3) is the number of 2subsets of X which have no exactly one element in common with Y.  _Milan Janjic_, Dec 28 2007
%D McKean and Moll, Elliptic Curves, 1997, Cambridge University Press, page 20.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,3,1).
%F a(n7)=1/2*n^29/2*n+16, n=7,8,9,...  _Milan Janjic_, Dec 28 2007
%t 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]
%Y Cf. A078907.
%K nonn,easy
%O 3,4
%A _Roger L. Bagula_, Jan 29 2006
%E Edited by _N. J. A. Sloane_, Apr 21 2007
