

A113920


G.f.: (x^3  x + 1)^3/(x^3*(1  x)^3).


0



1, 0, 0, 3, 3, 3, 6, 9, 12, 16, 21, 27, 34, 42, 51, 61, 72, 84, 97, 111, 126, 142, 159, 177, 196, 216, 237, 259, 282, 306, 331, 357, 384, 412, 441, 471, 502, 534, 567, 601, 636, 672, 709, 747, 786, 826, 867, 909, 952, 996, 1041, 1087, 1134, 1182, 1231, 1281, 1332, 1384, 1437
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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 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


REFERENCES

McKean and Moll, Elliptic Curves, 1997, Cambridge University Press, page 20.


LINKS

Table of n, a(n) for n=3..55.
Index entries for linear recurrences with constant coefficients, signature (3,3,1).


FORMULA

a(n7)=1/2*n^29/2*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]


CROSSREFS

Cf. A078907.
Sequence in context: A262877 A141094 A132972 * A081848 A079988 A212091
Adjacent sequences: A113917 A113918 A113919 * A113921 A113922 A113923


KEYWORD

nonn,easy


AUTHOR

Roger L. Bagula, Jan 29 2006


EXTENSIONS

Edited by N. J. A. Sloane, Apr 21 2007


STATUS

approved



