cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A091575 Poincaré series [or Poincare series] of the preprojective algebra of a Dynkin diagram of type E_8.

Original entry on oeis.org

8, 14, 20, 26, 32, 38, 44, 48, 52, 56, 60, 62, 64, 64, 64, 64, 64, 62, 60, 56, 52, 48, 44, 38, 32, 26, 20, 14, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Offset: 0

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Author

Paul Boddington, Jan 22 2004

Keywords

Examples

			The series is a polynomial because the algebra is finite dimensional. For an arbitrary Dynkin diagram the corresponding polynomial is (n+n*x^h-2*x^e_1-...-2*x^e_n)/(1-x)^2, where n is the rank, h the Coxeter number and e_1,...,e_n the Coxeter exponents of the associated Coxeter group.
		

References

  • I. Reiten, Dynkin diagrams and the representation theory of algebras, Notices of the AMS, Vol. 44, Number 5.

Crossrefs

A089011 a(n) = 1 if n is an exponent of the Weyl group W(E_7), 0 otherwise.

Original entry on oeis.org

1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Offset: 1

Views

Author

Paul Boddington, Nov 03 2003

Keywords

Comments

The exponents are 1, 5, 7, 9, 11, 13, 17. The point of this sequence is that a similar generating function gives the exponents for any finite Coxeter group.

Crossrefs

Programs

  • PARI
    {a(n)=if(n<1, 0, polcoeff( x^17+x^13+x^11+x^9+x^7+x^5+x, n))} /* Michael Somos, Mar 07 2007 */

Formula

Euler transform of length 14 sequence [ 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, -1, 0, -1]. - Michael Somos, Mar 07 2007
G.f.: x*(1-x^12)*(1-x^14)/((1-x^4)*(1-x^6)).
Showing 1-2 of 2 results.