A154645 -id:A154645 - cp's OEIS frontend

A139472 Incorrect version of A154641 and A154645.

1, 7, 76, 732, 6732, 62934

Offset: 1

dead

A154638 a(n) is the number of distinct reduced words of length n in the Coxeter group of "Apollonian reflections" in three dimensions.

1, 5, 20, 70, 240, 810, 2730, 9180, 30870, 103770, 348840, 1172610, 3941730, 13249980, 44539470, 149717970, 503272440, 1691734410, 5686712730, 19115706780, 64256852070, 215997400170, 726068516040, 2440656636210, 8204191055730, 27578131979580, 92703029288670

Offset: 0

Colin Mallows, Jan 13 2009

Definition means that all possible length-reducing cancellations have been applied and words that are equal are counted only once.
This group has five generators, satisfying (S_i)^2 = (S_i S_j)^3 = I.
ABA and BAB are equal, so are counted as only one distinct word.

			There are 80 squarefree words of length 3, but 20 of these fall into 10 equal pairs (e.g., ABA = BAB). So a(3)=70.

K. Brockhaus, Table of n, a(n) for n = 0..1000
R. L. Graham, J. C. Lagarias, C. L. Mallows, Allan Wilks and C. Yan, Apollonian circle Packings: Geometry and Group Theory III Higher Dimensions, arXiv:math/0010324 [math.MG], 2001-2005.
R. L. Graham, J. C. Lagarias, C. L. Mallows, Allan Wilks and C. Yan, Apollonian circle Packings: Geometry and Group Theory III Higher Dimensions, Discrete and Computational Geometry 35: 37-72 (2006).
C. L. Mallows, Growing Apollonian packings, J. Integer Sequences 12, article 09.2.1 (2009)
Index entries for linear recurrences with constant coefficients, signature (3, 3, -6).

For other sequences relating to the 3-dimensional case, see A154638-A154645.

/* gives growth function and terms of sequence - from Klaus Brockhaus, Feb 13 2010 */
G := Group< s1, s2, s3, s4, s5 | [ s1^2, s2^2, s3^2, s4^2, s5^2, (s1*s2)^3, (s1*s3)^3, (s1*s4)^3, (s1*s5)^3, (s2*s3)^3, (s2*s4)^3, (s2*s5)^3, (s3*s4)^3, (s3*s5)^3, (s4*s5)^3 ] >;
A := AutomaticGroup(G);
f := GrowthFunction(A); f;
T := PowerSeriesRing(Integers(), 27);
Eltseq(T!f);

CoefficientList[Series[(z^3 + 2 z^2 + 2 z + 1)/(6 z^3 - 3 z^2 - 3 z + 1), {z, 0, 100}], z] (* Vladimir Joseph Stephan Orlovsky, Jun 24 2011 *)
Join[{1},LinearRecurrence[{3,3,-6},{5,20,70},30]] (* Harvey P. Dale, Nov 16 2011 *)

a(n)=if(n,([0,1,0;0,0,1;-6,3,3]^n*[5/6;5;20])[1,1],1) \\ Charles R Greathouse IV, Jun 11 2015

There's a handy program (or rather, a constellation of programs), kbmag by Derek Holt et al., which can be used as a package within GAP or as a free-standing program, to try to find an automatic structure for a group. I entered this presentation, and it produced an automatic structure, which implies the growth function is rational: (1 + 2*X + 2*X^2 + X^3)/(1 - 3*X - 3*X^2 + 6*X^3), as reported by kbgrowth. John Cannon also found this g.f. - William P. Thurston, Nov 22 2009

Recurrence: for n >= 1, a(n+3) = 3*a(n+2) + 3*a(n+1) - 6*a(n) with a(0..3)={1,5,20,70}. - Zak Seidov, Dec 07 2009

Corrected and extended with g.f. by John Cannon and William P. Thurston, Nov 22 2009

Edited by N. J. A. Sloane, Nov 22 2009

A154636 a(n) is the ratio of the sum of the bends of the circles that are drawn in the n-th generation of Apollonian packing to the sum of the bends of the circles in the initial configuration of 3 circles.

Original entry on oeis.org

1, 2, 18, 138, 1050, 7986, 60738, 461946, 3513354, 26720994, 203227890, 1545660138, 11755597434, 89407799058, 679995600162, 5171741404122, 39333944432490, 299156331247554, 2275248816682962, 17304521539721034, 131610425867719386, 1000969842322591986

Offset: 0

Colin Mallows, Jan 13 2009

For comments and more references and links, see A189226.

			Starting from three circles with bends -1,2,2 summing to 3, the first derived generation consists of two circles, each with bend 3. So a(1) is (3+3)/3 = 2.

Colin Barker, Table of n, a(n) for n = 0..1000
C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.
Index entries for linear recurrences with constant coefficients, signature (8,-3).

Other sequences relating to the two-dimensional case are A135849, A137246, A154637. For the three-dim. case see A154638 - A154645. Five dimensions: A154635.

Cf. also A189226, A189227.

CoefficientList[Series[(5 z^2 - 6 z + 1)/(3 z^2 - 8 z + 1), {z, 0, 100}], z] (* and *) LinearRecurrence[{8, -3}, {1, 2, 18}, 100] (* Vladimir Joseph Stephan Orlovsky, Jul 03 2011 *)

Vec((1 - x)*(1 - 5*x) / (1 - 8*x + 3*x^2) + O(x^30)) \\ Colin Barker, Jul 15 2017

G.f.: (1 - x)*(1 - 5*x) / (1 - 8*x + 3*x^2).
From Colin Barker, Jul 15 2017: (Start)
a(n) = ((-(-7+sqrt(13))*(4+sqrt(13))^n - (4-sqrt(13))^n*(7+sqrt(13)))) / (3*sqrt(13)) for n>0.
a(n) = 8*a(n-1) - 3*a(n-2) for n>2.
(End)

More terms from N. J. A. Sloane, Nov 22 2009

A154637 a(n) is the ratio of the sum of squares of the bends of the circles that are added in the n-th generation of Apollonian packing, to the sum of squares of the bends of the initial three circles.

Original entry on oeis.org

1, 2, 66, 1314, 26082, 517698, 10275714, 203961186, 4048396578, 80356048002, 1594975770306, 31658447262114, 628384017931362, 12472705016840898, 247568948283023874, 4913960850609954786, 97536510167350024098, 1935988320795170617602, 38427156885401362279746, 762735172745641733742114

Offset: 0

Colin Mallows, Jan 13 2009

For more references and links, see A189226.

			Starting with three circles with bends -1,2,2, the ssq is 9. The first derived generation has two circles, each with bend 3. So a(1) = (9+9)/9 = 2.

Colin Barker, Table of n, a(n) for n = 0..750
Colin Mallows, Growing Apollonian packings, J. Integer Sequences v.12, article 09.2.1 (2009).
Index entries for linear recurrences with constant coefficients, signature (20,-3).

For starting with four circles, see A137246. For sums of bends, see A135849 and A154636. For three dimensions, see A154638 - A154645.

Cf. also A189226, A189227.

CoefficientList[Series[(29 z^2 - 18 z + 1)/(3 z^2 - 20 z + 1), {z, 0, 100}], z] (* and *) LinearRecurrence[{20, -3}, {1, 2, 66}, 100] (* Vladimir Joseph Stephan Orlovsky, Jul 03 2011 *)

Vec((1-18*x+29*x^2)/(1-20*x+3*x^2) + O(x^30)) \\ Colin Barker, Nov 16 2016

G.f.: (1-18*x+29*x^2) / (1-20*x+3*x^2).
From Colin Barker, Nov 16 2016: (Start)
a(n) = ((133-13*sqrt(97))*(10+sqrt(97))^n - (10-sqrt(97))^n*(133+13*sqrt(97))) / (3*sqrt(97)) for n>0.
a(n) = 20*a(n-1) - 3*a(n-2) for n>2.
(End)

More terms from N. J. A. Sloane, Nov 22 2009

A154635 Ratio of the sum of the bends of the 5-dimensional spheres added in the n-th generation of Apollonian packing to the sum of the bends of the initial configuration of seven mutually tangent spheres.

Original entry on oeis.org

1, 2, 15, 108, 774, 5544, 39708, 284400, 2036952, 14589216, 104492016, 748400832, 5360254560, 38391631488, 274971524544, 1969422407424, 14105550112128, 101027866452480, 723589630947072, 5182549848861696, 37118861005211136, 265855588948518912

Offset: 0

Colin Mallows, Jan 13 2009

			Starting with seven 5-dimensional spheres with bends 0,0,1,1,1,1,1 summing to 5, the first derived generation has seven spheres, with bends 1,1,1,1,1,5/2,5/2 summing to 10. So a(1) = 10/5 = 2.

Colin Barker, Table of n, a(n) for n = 0..1000
Colin Mallows, Growing Apollonian packings, J. Integer Sequences v.12, article 09.2.1 (2009).
Index entries for linear recurrences with constant coefficients, signature (8,-6).

Cf. A135849 for dim=2. A137146 for the sum of squares of bends when dim=2. A154636 and A154637 for starting with three spheres in 2 dimensions. A154638-A154645 for results in the three-dimensional case.

CoefficientList[Series[(1 - z) (1 - 5 z)/(1 - 8 z + 6 z^2), {z, 0, 100}], z] (* Vladimir Joseph Stephan Orlovsky, Jul 03 2011 *)

Vec((1-x)*(1-5*x)/(1-8*x+6*x^2) + O(x^30)) \\ Colin Barker, Nov 16 2016

G.f. (1-x)*(1-5*x) / (1-8*x+6*x^2).
From Colin Barker, Nov 16 2016: (Start)
a(n) = (((4-sqrt(10))^n*(-8+sqrt(10))+(4+sqrt(10))^n*(8+sqrt(10))))/(12*sqrt(10)) for n>0.
a(n) = 8*a(n-1) - 6*a(n-2) for n>2.
(End)

A154641 a(n) is the ratio of the sum of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (a)" to count them (see the reference), to the sum of the bends of the initial five mutually tangent spheres.

Original entry on oeis.org

1, 3, 20, 108, 630, 3570, 20460

Offset: 0

Colin Mallows, Jan 13 2009

In strategy (a) we do not count spheres that can be obtained (by reflection) from the "extra" quintuples of spheres that appear in the previous generation.

			Starting with five spheres with bends 0,0,1,1,1, the first derived generation has 5 spheres with bends 1,1,1,3,3, so a(2) = 9/3 = 3.

C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.

For other sequences relating to the 3-dimensional case, see A154638-A154645.

A154644 a(n) is the ratio of the sum of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (b)" to count them (see the reference), to the sum of the bends of the initial five mutually tangent spheres.

Original entry on oeis.org

1, 3, 20, 174, 1170, 8454

Offset: 0

Colin Mallows, Jan 13 2009

In strategy (b) we count all spheres that can be generated (by reflection) from all quintuples that appeared in the previous generation.

			Starting with five spheres with bends 0,0,1,1,1, the first derived generation has 5 spheres with bends 1,1,1,3,3, so a(2) = 9/3 = 3.

C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.

For other sequences relating to the 3-dimensional case, see A154638-A154645.

A154639 a(n) is the number of reduced words of length n (i.e., all possible length-reducing cancellations have been applied) in the generators of the "Apollonian reflection group" in three dimensions. This is a Coxeter group with five generators, satisfying the identities (S_i)^2 = (S_i S_j)^3 = I.

Original entry on oeis.org

1, 5, 20, 80, 300, 1140, 4260

Offset: 0

Colin Mallows, Jan 13 2009

ABA and BAB are equal, but are counted as distinct reduced words.

			All 80 squarefree words of length 3 are counted, so a(3) = 80.

R. L. Graham, J. C. Lagarias, C. L. Mallows, Allan Wilks and C. Yan, Apollonian Circle Packings: Geometry and Group Theory III. Higher Dimensions., Discrete & Computational Geometry, 35 (2006), no. 1, 37-72.
C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.

For other sequences relating to the 3-dimensional case, see A154638-A154645.

A154640 a(n) is the number of spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, starting with five mutually tangent spheres and using "strategy (a)" to count them (see the reference).

Original entry on oeis.org

5, 5, 20, 60, 210, 690, 3330

Offset: 0

Colin Mallows, Jan 13 2009

In strategy (a) we do not count spheres that are generated (by reflection) from quintuples that were not generated in the previous generation.

			For a(3), we apply reflection only to the 20 quintuples that were generated in the second generation, ignoring the 10 "extra" quintuples (which will appear as ABA = BAB in the third generation).

C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.

For other sequences relating to the 3-dimensional case, see A154638-A154645.

A154642 a(n) is the ratio of the sum of the squares of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (a)" to count them (see the reference), to the sum of the squares of the bends of the initial five mutually tangent spheres.

Original entry on oeis.org

1, 6, 77, 732, 7278, 71634, 707076

Offset: 0

Colin Mallows, Jan 13 2009

In strategy (a) we do not count spheres that can be obtained (by reflection) from the "extra" quintuples of spheres that appear in the previous generation.

			Starting with five spheres with bends 0,0,1,1,1, the first derived generation has 5 spheres with bends 1,1,1,3,3, so a(2) = 9/3 = 3.

C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.

For other sequences relating to the 3-dimensional case, see A154638-A154645.

cp's OEIS Frontend

A139472 Incorrect version of A154641 and A154645.

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A154638 a(n) is the number of distinct reduced words of length n in the Coxeter group of "Apollonian reflections" in three dimensions.

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A154636 a(n) is the ratio of the sum of the bends of the circles that are drawn in the n-th generation of Apollonian packing to the sum of the bends of the circles in the initial configuration of 3 circles.

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A154637 a(n) is the ratio of the sum of squares of the bends of the circles that are added in the n-th generation of Apollonian packing, to the sum of squares of the bends of the initial three circles.

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Mathematica

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A154635 Ratio of the sum of the bends of the 5-dimensional spheres added in the n-th generation of Apollonian packing to the sum of the bends of the initial configuration of seven mutually tangent spheres.

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Programs

Mathematica

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Formula

A154641 a(n) is the ratio of the sum of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (a)" to count them (see the reference), to the sum of the bends of the initial five mutually tangent spheres.

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Author

Keywords

Comments

Examples

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Crossrefs

A154644 a(n) is the ratio of the sum of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (b)" to count them (see the reference), to the sum of the bends of the initial five mutually tangent spheres.

Views

Author

Keywords

Comments

Examples

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Crossrefs

A154639 a(n) is the number of reduced words of length n (i.e., all possible length-reducing cancellations have been applied) in the generators of the "Apollonian reflection group" in three dimensions. This is a Coxeter group with five generators, satisfying the identities (S_i)^2 = (S_i S_j)^3 = I.

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Author

Keywords

Comments

Examples

Links

Crossrefs