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A001471 Number of degree-n permutations of order exactly 3.
(Formerly M1833 N0727)
26
0, 0, 0, 2, 8, 20, 80, 350, 1232, 5768, 31040, 142010, 776600, 4874012, 27027728, 168369110, 1191911840, 7678566800, 53474964992, 418199988338, 3044269834280, 23364756531620, 199008751634000, 1605461415071822 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 0..100

L. Moser and M. Wyman, On solutions of x^d = 1 in symmetric groups, Canad. J. Math., 7 (1955), 159-168.

FORMULA

From Henry Bottomley, Jan 26 2001: (Start)

a(n) = a(n-1) + (1 + a(n-3))*(n-1)(n-2).

a(n) = Sum_{j=1..floor(n/3)} n!/(j!*(n-3*j)!*(3^j)).

a(n) = A001470(n) - 1. (End)

E.g.f.: exp(x + x^3/3) - exp(x).

MATHEMATICA

a[n_] := HypergeometricPFQ[{1/3-n/3, 2/3-n/3, -n/3}, {}, -9] - 1; Table[a[n], {n, 0, 23}] (* Jean-François Alcover, Oct 19 2011 *)

PROG

(PARI) a(n)=sum(j=1, n\3, n!/(j!*(n-3*j)!*(3^j))) \\ Charles R Greathouse IV, Jun 21 2017

(MAGMA) m:=30; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!( Exp(x + x^3/3) )); [Factorial(n-1)*b[n]-1: n in [1..m]]; // G. C. Greubel, May 14 2019

(Sage) m = 30; T = taylor(exp(x + x^3/3) -exp(x), x, 0, m); [factorial(n)*T.coefficient(x, n) for n in (0..m)] # G. C. Greubel, May 14 2019

CROSSREFS

Cf. A000085, A001470, A001472, A052501, A053496-A053505, A001189, A001471, A001473, A061121-A061128.

Column k=3 of A057731.

Sequence in context: A133467 A091004 A005559 * A162585 A000159 A090612

Adjacent sequences:  A001468 A001469 A001470 * A001472 A001473 A001474

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane and J. H. Conway

STATUS

approved

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Last modified October 19 14:54 EDT 2019. Contains 328223 sequences. (Running on oeis4.)