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 A120747 Sequence relating to the hendecagon (11-gon). 4
 0, 1, 4, 14, 50, 175, 616, 2163, 7601, 26703, 93819, 329615, 1158052, 4068623, 14294449, 50221212, 176444054, 619907431, 2177943781, 7651850657, 26883530748, 94450905714, 331837870408, 1165858298498, 4096053203771, 14390815650209, 50559786403254 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The hendecagon is an 11-sided polygon, see Weisstein. The lengths of the diagonals of the regular hendecagon are r[k] = sin(k*Pi/11)/sin(Pi/11), 1 <= k <= 5, where r[1] = 1 is the length of the edge. The value of limit(a(n)/a(n-1),n=infinity) equals the longest diagonal r[5]. The a(n) equal the matrix elements M^n[1,2], where M = Matrix([[1,1,1,1,1], [1,1,1,1,0], [1,1,1,0,0], [1,1,0,0,0], [1,0,0,0,0]]). The characteristic polynomial of M is (x^5 - 3x^4 - 3x^3 + 4x^2 + x - 1) with roots x1 = -r[4]/r[3], x2 = -r[2]/r[4], x3 = r[1]/r[2], x4 = r[3]/r[5] and x5 = r[5]/r[1]. Note that M^4*[1,0,0,0,0] = [55, 50, 41, 29, 15] which are all terms of the 5-wave sequence A038201. This is also the case for the terms of M^n*[1,0,0,0,0], n>=1. REFERENCES Steinbach Peter, Golden Fields: A case for the heptagon, Mathematics Magazine 70 (1997) pp. 22-31. LINKS Eric W. Weisstein, Hendecagon , Wolfram Mathworld. Jay Kappraff, Slavik Jablan, Gary W. Adamson and Radmila Sazdanovich, Golden Fields, Generalized Fibonacci Sequences and Chaotic Matrices , Forma, Vol. 19 No. 4, pp. 367-387, 2004. FORMULA a(n) = 3*a(n-1) + 3*a(n-2) - 4*a(n-3) - a(n-4) + a(n-5). G.f.: x^2*(1+x-x^2)/(1-3*x-3*x^2+4*x^3+x^4-x^5) [From Maksym Voznyy (voznyy(AT)mail.ru), Aug 12 2009] From Johannes W. Meijer, Aug 3 2011: (Start) a(n) = T(n,4) with T(n,k) = sum(T(n-1,k1), k1=6-k..5), T(1,1) = T(1,2) = T(1,3) = T(1,4) = 0 and T(1,5) = 1, n>=1 and 1 <= k <= 5. [Steinbach] sum(T(n,k)*r[k], k=1..5) = r[5]^n, n>=1. [Steinbach] r[k] = sin(k*Pi/11)/sin(Pi/11), 1 <= k <= 5. [Kappraff] sum(T(n,k), k=1..5) = A006358(n-1) limit(T(n,k)/T(n-1,k), n = infinity) = r[5], 1 <= k <= 5. sequence(sequence(T(n,k), k=2..5), n>=1) = A038201(n-4) G.f.: (x^2*(x-x1)*(x-x2))/((x-x3)*(x-x4)*(x-x5)*(x-x6)*(x-x7)) with x1 = phi, x2 = (1-phi), x3 = r[1]-r[3], x4 = r[3]-r[5], x5 = r[5]-r[4], x6 = r[4]-r[2], x7 = r[2], where phi = (1 + sqrt(5))/2 is the golden ratio A001622. (End) EXAMPLE From Johannes W. Meijer, Aug 3 2011: (Start) The lengths of the regular hendecagon edge and diagonals are: r[1] = 1.000000000, r[2] = 1.918985948, r[3] = 2.682507066, r[4] = 3.228707416, r[5] = 3.513337092 The first few rows of the T(n,k) array are, n>=1, 1 <= k <=5: 0,   0,   0,   0,   1 1,   1,   1,   1,   1 1,   2,   3,   4,   5 5,   9,   12,  14,  15 15,  29,  41,  50,  55 55,  105, 146, 175, 190 190, 365, 511, 616, 671 (End) MAPLE nmax:=27: m:=5: for k from 1 to m-1 do T(1, k):=0 od: T(1, m):=1: for n from 2 to nmax do for k from 1 to m do T(n, k):= add(T(n-1, k1), k1=m-k+1..m) od: od: for n from 1 to nmax/3 do seq(T(n, k), k=1..m) od; for n from 1 to nmax do a(n):=T(n, 4) od: seq(a(n), n=1..nmax); [Johannes W. Meijer, Aug 03 2011] CROSSREFS Cf. A038201, A006358, A038342, A069006, A066170, A065941, A052963, A033304. From Johannes W. Meijer, Aug 03 2011: (Start) Cf. A006358 (T(n+2,1) and T(n+1,5)), A069006 (T(n+1,2)), A038342 (T(n+1,3)), A120747 (T(n,4)) (m=5: hendecagon or 11-gon) Cf. A000045 (m=2; pentagon or 5-gon); A006356, A006054 and A038196 (m=3: heptagon or 7-gon); A006357, A076264, A091024 and A038197 (m=4: enneagon or 9-gon); A006359, A069007, A069008, A069009, A070778 (m=6; tridecagon or 13-gon); A025030 (m=7: pentadecagon or 15-gon); A030112 (m=8: heptadecagon or 17-gon). (End) Sequence in context: A079309 A026630 A034459 * A055099 A153367 A211304 Adjacent sequences:  A120744 A120745 A120746 * A120748 A120749 A120750 KEYWORD nonn,easy AUTHOR Gary W. Adamson, Jul 01 2006 EXTENSIONS Edited and information added by Johannes W. Meijer, Aug 03 2011 STATUS approved

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