login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A007043 Number of noncommutative SL(2,C)-invariants of degree n in 5 variables.
(Formerly M3870)
11
1, 0, 1, 1, 5, 16, 65, 260, 1085, 4600, 19845, 86725, 383251, 1709566, 7687615, 34812519, 158614405, 726612216, 3344696501, 15462729645, 71763732545, 334236300200, 1561686608685, 7318223046860, 34386154568375, 161970182441556, 764676831501575, 3617755131480841 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,5
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Gert Almkvist, Warren Dicks, and Edward Formanek, Hilbert series of fixed free algebras and noncommutative classical invariant theory, J. Algebra 93 (1985), no. 1, 189-214.
Eliahu Cohen, Tobias Hansen, and Nissan Itzhaki, From Entanglement Witness to Generalized Catalan Numbers, arXiv:1511.06623 [quant-ph], 2015.
Thomas Curtright, T. S. Van Kortryk, and Cosmas Zachos, Spin Multiplicities, hal-01345527, 2016.
R. K. Guy, Parker's permutation problem involves the Catalan numbers, preprint, 1992. (Annotated scanned copy)
FORMULA
From Paul Barry, Oct 18 2007: (Start)
a(n) = Sum{k=0..n} Sum{j=0..k} C(n,k)*C(k,j)*(-3)^(k-j)*A000108(j);
a(n) = (1/(2*Pi))*Integral_{x=0..4} (1 - 3*x + x^2)^n*sqrt(x*(4 - x))/x dx. (End)
G.f.: F(G^(-1)(x)), where F(t) := (t^2 + 3*t + 1)/((t + 1)*(4*t + 1)^(1/2)) and G(t) := t/(t^2 + 3*t + 1). - Mark van Hoeij, Oct 30 2011
a(n) ~ 5^n/(8*sqrt(Pi)*n^(3/2)) * (1 - 15/(16*n) + O(1/n^2)). - Thomas Curtright, Jun 17 2016, updated Jul 26 2016
D-finite with recurrence: 2*n*(2*n + 1)*(3*n - 5)*a(n) = (n-1)*(3*n - 2)*(19*n - 20)*a(n-1) + 10*(n-1)*n*(3*n - 5)*a(n-2) - 25*(n-2)*(n-1)*(3*n - 2)*a(n-3). - Vaclav Kotesovec, Jun 24 2016
a(n) = (1/Pi)*Integral_{x=0..2*Pi} (sin(5*x)/sin(x))^n*(sin(x))^2. - Thomas Curtright, Jun 24 2016
MAPLE
F := (t^2+3*t+1)/((t+1)*(4*t+1)^(1/2)); G := t/(t^2+3*t+1); Ginv := RootOf(numer(G-x), t); ogf := series(eval(F, t=Ginv), x=0, 20); # Mark van Hoeij, Oct 30 2011
MATHEMATICA
CoefficientList[Series[Sqrt[2]/Sqrt[(1 - x)*((1 + 5*x) + Sqrt[(1 - 5*x)*(1 - x)])], {x, 0, 20}], x] (* Vaclav Kotesovec, Jun 24 2016, after Almkvist, Dicks and Formanek *)
a[n_]:= c[0, n, 2]-c[1, n, 2]; c[j_, n_, s_]:= Sum[(-1)^k*Binomial[n, k]*Binomial[j - (2*s + 1)*k + n + n*s - 1, j - (2*s + 1)*k + n*s], {k, 0, Min[n, Floor[(j + n*s)/(2*s + 1)]]}]; Table[a[n], {n, 0, 20}] (* Thomas Curtright, Jul 26 2016 *)
CROSSREFS
Cf. A000108, A348210 (column k=2).
Sequence in context: A301958 A349568 A026525 * A128242 A323934 A166932
KEYWORD
nonn
AUTHOR
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 08:08 EDT 2024. Contains 371265 sequences. (Running on oeis4.)