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 A241606 A linear divisibility sequence of the fourth order related to A003779. 2
 1, 11, 95, 781, 6336, 51205, 413351, 3335651, 26915305, 217172736, 1752296281, 14138673395, 114079985111, 920471087701, 7426955448000, 59925473898301, 483517428660911, 3901330906652795, 31478457514091281, 253988526230055936 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A003779, which counts spanning trees in the graph P_5 x P_n, is a linear divisibility sequence of order 16. It factors into two fourth-order linear divisibility sequences; this sequence is one of the factors, the other is A143699. The present sequence is the case P1 = 11, P2 = 23, Q = 1 of the 3 parameter family of 4th order linear divisibility sequences found by Williams and Guy. LINKS H. C. Williams and R. K. Guy, Some fourth-order linear divisibility sequences, Intl. J. Number Theory 7 (5) (2011) 1255-1277. H. C. Williams and R. K. Guy, Some Monoapparitic Fourth Order Linear Divisibility Sequences Integers, Volume 12A (2012) The John Selfridge Memorial Volume Index entries for linear recurrences with constant coefficients, signature (11,-25,11,-1). FORMULA O.g.f. x*(1 - x^2)/(1 - 11*x + 25*x^2 - 11*x^3 + x^4). a(n) = A003779(n)/A143699(n). a(n) = ( T(n,alpha) - T(n,beta) )/(alpha - beta), n >= 1, where alpha = 1/4*(11 + sqrt(29)), beta = 1/4*(11 - sqrt(29)) and where T(n,x) denotes the Chebyshev polynomial of the first kind. a(n)= U(n-1,1/4*(7 - sqrt(5)))*U(n-1,1/4*(7 + sqrt(5))), n >= 1, where U(n,x) denotes the Chebyshev polynomial of the second kind. a(n) = the bottom left entry of the 2X2 matrix T(n,M), where M is the 2 X 2 matrix [0, -23/4; 1, 11/2]. See the remarks in A100047 for the general connection between Chebyshev polynomials of the first kind and 4th order linear divisibility sequences. a(n) = 11*a(n-1) - 25*a(n-2) + 11*a(n-3) - a(n-4). - Vaclav Kotesovec, Apr 28 2014 MATHEMATICA a[n_] := ChebyshevU[n-1, 1/4*(7-Sqrt)]*ChebyshevU[n-1, 1/4*(7+Sqrt)]; Table[a[n]//Round, {n, 1, 20}] (* Jean-François Alcover, Apr 28 2014, after Peter Bala *) CROSSREFS Cf. A003779, A100047, A143699. Sequence in context: A164547 A298925 A016203 * A326349 A318599 A051446 Adjacent sequences:  A241603 A241604 A241605 * A241607 A241608 A241609 KEYWORD nonn,easy AUTHOR Peter Bala, Apr 26 2014 STATUS approved

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Last modified February 21 20:35 EST 2020. Contains 332111 sequences. (Running on oeis4.)