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A054621 Number of ways to color vertices of a heptagon using <= n colors, allowing only rotations. 4
0, 1, 20, 315, 2344, 11165, 39996, 117655, 299600, 683289, 1428580, 2783891, 5118840, 8964085, 15059084, 24408495, 38347936, 58619825, 87460020, 127695979, 182857160, 257298381, 356336860, 486403655, 655210224, 871930825, 1147401476, 1494336195, 1927561240 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Length-7 necklaces with n kinds of beads. - Vincenzo Librandi Apr 30 2012

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1).

FORMULA

a(n) = (1/7) * Sum_{d|7} phi(d)*n^(7/d) = (1/7) * (n^7 + 6*n). [corrected by Klaus Wagner, Sep 15 2015]

G.f.: x*(1+12*x+183*x^2+328*x^3+183*x^4+12*x^5+x^6) / (1-x)^8. - R. J. Mathar, Aug 30 2011

a(n) = 8*a(n-1)-28*a(n-2)+56*a(n-3)-70*a(n-4)+56*a(n-5)-28*a(n-6)+8*a(n-7)-a(n-8), n>7. - Wesley Ivan Hurt, Sep 15 2015

MAPLE

a:=proc(n) option remember:

if n=0 then 0 elif n=1 then 1 elif n=2 then 20 elif n=3 then 315 elif n=4 then 2344 elif n=5 then 11165 elif n=6 then 39996 elif n=7 then 117655 elif n=8 then 299600 else

8*a(n-1)-28*a(n-2)+56*a(n-3)-70*a(n-4)+56*a(n-5)-28*a(n-6)+8*a(n-7)-a(n-8): fi: end: seq(a(n), n=0..50); # Wesley Ivan Hurt, Sep 15 2015

MATHEMATICA

CoefficientList[Series[x*(1+12*x+183*x^2+328*x^3+183*x^4+ 12*x^5+x^6)/(x-1)^8, {x, 0, 33}], x] (* Vincenzo Librandi, Apr 30 2012 *)

PROG

(MAGMA) I:=[0, 1, 20, 315, 2344, 11165, 39996, 117655]; [n le 8 select I[n] else 8*Self(n-1)-28*Self(n-2)+56*Self(n-3)-70*Self(n-4)+56*Self(n-5)-28*Self(n-6)+8*Self(n-7)-Self(n-8): n in [1..30]]; // Vincenzo Librandi, Apr 30 2012

CROSSREFS

Cf. A054622. Row 7 of A075195.

Sequence in context: A281931 A034094 A011197 * A111778 A024387 A307173

Adjacent sequences:  A054618 A054619 A054620 * A054622 A054623 A054624

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Apr 16 2000

EXTENSIONS

Edited by Christian G. Bower, Sep 07 2002

STATUS

approved

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Last modified September 16 08:53 EDT 2019. Contains 327092 sequences. (Running on oeis4.)