

A118264


Coefficient of q^n in (1q)^3/(13q); dimensions of the enveloping algebra of the derived free Lie algebra on 3 letters.


3



1, 0, 3, 8, 24, 72, 216, 648, 1944, 5832, 17496, 52488, 157464, 472392, 1417176, 4251528, 12754584, 38263752, 114791256, 344373768, 1033121304, 3099363912, 9298091736, 27894275208, 83682825624, 251048476872, 753145430616
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OFFSET

0,3


COMMENTS

a(n) is the number of generalized compositions of n when there are i^21 different types of i, (i=1,2,...).  Milan Janjic, Sep 24 2010


REFERENCES

C. Reutenauer, Free Lie algebras. London Mathematical Society Monographs. New Series, 7. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1993. xviii+269 pp.


LINKS

Table of n, a(n) for n=0..26.
N. Bergeron, C. Reutenauer, M. Rosas and M. Zabrocki, Invariants and Coinvariants of the Symmetric Group in Noncommuting Variables, arXiv:math.CO/0502082 , Canad. J. Math. 60 (2008), no. 2, 266296.
Index entries for linear recurrences with constant coefficients, signature (3).


FORMULA

G.f.: (1x)^3/(13x).
a(n) = 3^{n1}3^{n3} for n>=3.
a(n) = A080923(n1), n>1.
If p[i]=i^21 and if A is Hessenberg matrix of order n defined by: A[i,j]=p[ji+1], (i<=j), A[i,j]=1, (i=j+1), and A[i,j]=0 otherwise. Then, for n>=1, a(n)=det A.  Milan Janjic, May 02 2010
For a(n)>=8, a(n+1)=3*a(n).  Harvey P. Dale, Jun 28 2011


EXAMPLE

The enveloping algebra of the derived free Lie algebra is characterized as the intersection of the kernels of all partial derivative operators in the space of noncommutative polynomials, a(0) = 1 since all constants are killed by derivatives, a(1) = 0 since no polys of degree 1 are killed, a(2) = 3 since all Lie brackets [x1,x2], [x1,x3], [x2, x3] are killed by all derivative operators.


MAPLE

f:=n>coeftayl((1q)^3/(13*q), q=0, n):seq(f(i), i=0..15);


MATHEMATICA

CoefficientList[Series[(1q)^3/(13q), {q, 0, 30}], q] (* or *) Join[{1, 0, 3}, NestList[3#&, 8, 30]] (* Harvey P. Dale, Jun 28 2011 *)
Join[{1, 0, 3}, LinearRecurrence[{3}, {8}, 24]] (* JeanFrançois Alcover, Sep 23 2017 *)


CROSSREFS

Cf. A080923, A027376, A118265, A118266.
Sequence in context: A052855 A133787 A080923 * A006365 A178543 A188175
Adjacent sequences: A118261 A118262 A118263 * A118265 A118266 A118267


KEYWORD

nonn,easy


AUTHOR

Mike Zabrocki, Apr 20 2006


EXTENSIONS

Formula corrected Mike Zabrocki, Jul 22 2010


STATUS

approved



