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A008627 Molien series for A_4. 1
1, 1, 2, 3, 5, 6, 10, 12, 17, 21, 28, 33, 43, 50, 62, 72, 87, 99, 118, 133, 155, 174, 200, 222, 253, 279, 314, 345, 385, 420, 466, 506, 557, 603, 660, 711, 775, 832, 902, 966, 1043, 1113, 1198, 1275, 1367, 1452, 1552, 1644, 1753, 1853, 1970, 2079, 2205, 2322 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

With offset = 4: a(n) is the number of equivalence classes of compositions (summands >=1) of n into exactly 4 parts where two compositions a,b are considered equivalent if the summands of a can be permuted into the summands of b with an even number of transpositions.  For example, let the class representatives be the last such composition in lexicographic order.  a(10)=10 because we have the following nine partitions of 10 into 4 parts, {7,1,1,1}, {6,2,1,1}, {5,3,1,1}, {5,2,2,1}, {4,4,1,1}, {4,3,2,1}, {4,2,2,2},{3,3,3,1}, {3,3,2,2} and the class represented by {3,4,2,1}. - Geoffrey Critzer, Oct 16 2012

REFERENCES

D. J. Benson, Polynomial Invariants of Finite Groups, Cambridge, 1993, p. 105.

LINKS

Table of n, a(n) for n=0..53.

Index entries for Molien series

Index entries for linear recurrences with constant coefficients, signature (1,2,-1,-2,-1,2,1,-1).

FORMULA

a(n) ~ 1/72*n^3. - Ralf Stephan, Apr 29 2014

G.f.: ( 1-x^2+x^4 ) / ( (1+x+x^2)*(1+x)^2*(x-1)^4 ). - R. J. Mathar, Dec 18 2014

MAPLE

(1+x^6)/(1-x)/(1-x^2)/(1-x^3)/(1-x^4): seq(coeff(series(%, x, n+1), x, n), n=0..60);

MATHEMATICA

nn=50; CoefficientList[Series[CycleIndex[AlternatingGroup[4], s]/.Table[s[i]->x^i/(1-x^i), {i, 1, nn}], {x, 0, nn}], x]  (* Geoffrey Critzer, Oct 16 2012 *)

PROG

(Sage) SR(AlternatingGroup(4).molien_series()).series(x, 20) # Ralf Stephan, Apr 29 2014

CROSSREFS

Sequence in context: A191173 A240026 A213212 * A027593 A007211 A130900

Adjacent sequences:  A008624 A008625 A008626 * A008628 A008629 A008630

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified March 25 10:22 EDT 2019. Contains 321470 sequences. (Running on oeis4.)