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 A057080 Even-indexed Chebyshev U-polynomials evaluated at sqrt(10)/2. 23

%I

%S 1,9,71,559,4401,34649,272791,2147679,16908641,133121449,1048062951,

%T 8251382159,64962994321,511452572409,4026657584951,31701808107199,

%U 249587807272641,1965000650073929,15470417393318791,121798338496476399

%N Even-indexed Chebyshev U-polynomials evaluated at sqrt(10)/2.

%C a(n) = L(n,-8)*(-1)^n, where L is defined as in A108299; see also A070997 for L(n,+8). - _Reinhard Zumkeller_, Jun 01 2005

%C General recurrence is a(n)=(a(1)-1)*a(n-1)-a(n-2), a(1)>=4, lim n->infinity a(n)= x*(k*x+1)^n, k =(a(1)-3), x=(1+sqrt((a(1)+1)/(a(1)-3)))/2. Examples in OEIS: a(1)=4 gives A002878. a(1)=5 gives A001834. a(1)=6 gives A030221. a(1)=7 gives A002315. a(1)=8 gives A033890. a(1)=9 gives A057080. a(1)=10 gives A057081. [From _Ctibor O. Zizka_, Sep 02 2008]

%C The primes in this sequence are 71, 34649, 16908641, 8251382159, 31701808107199,... - _Ctibor O. Zizka_, Sep 02 2008

%C The aerated sequence (b(n))n>=1 = [1, 0, 9, 0, 71, 0, 559, 0, ...] is a fourth-order linear divisibility sequence; that is, if n | m then b(n) | b(m). It is the case P1 = 0, P2 = -6, Q = -1 of the 3-parameter family of divisibility sequences found by Williams and Guy. See A100047. - _Peter Bala_, Mar 22 2015

%D Fink, Alex, Richard Guy, and Mark Krusemeyer. "Partitions with parts occurring at most thrice." Contributions to Discrete Mathematics 3.2 (2008), 76-114. See Section 13.

%H G. C. Greubel, <a href="/A057080/b057080.txt">Table of n, a(n) for n = 0..1000</a>

%H Marco Abrate, Stefano Barbero, Umberto Cerruti, Nadir Murru, <a href="https://www.emis.de/journals/INTEGERS/papers/p38/p38.Abstract.html">Polynomial sequences on quadratic curves</a>, Integers, Vol. 15, 2015, #A38.

%H Andersen, K., Carbone, L. and Penta, D., <a href="https://pdfs.semanticscholar.org/8f0c/c3e68d388185129a56ed73b5d21224659300.pdf">Kac-Moody Fibonacci sequences, hyperbolic golden ratios, and real quadratic fields</a>, Journal of Number Theory and Combinatorics, Vol 2, No. 3 pp 245-278, 2011. See Section 9.

%H Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>

%H W. Lang, <a href="http://www.fq.math.ca/Scanned/38-5/lang.pdf">On polynomials related to powers of the generating function of Catalan's numbers</a>, Fib. Quart. 38 (2000) 408-419. Eq.(44), rhs, m=10.

%H Donatella Merlini and Renzo Sprugnoli, <a href="https://doi.org/10.1016/j.disc.2016.08.017">Arithmetic into geometric progressions through Riordan arrays</a>, Discrete Mathematics 340.2 (2017): 160-174.

%H H. C. Williams and R. K. Guy, <a href="http://dx.doi.org/10.1142/S1793042111004587">Some fourth-order linear divisibility sequences</a>, Intl. J. Number Theory 7 (5) (2011) 1255-1277.

%H H. C. Williams and R. K. Guy, <a href="http://www.emis.de/journals/INTEGERS/papers/a17self/a17self.Abstract.html">Some Monoapparitic Fourth Order Linear Divisibility Sequences</a> Integers, Volume 12A (2012) The John Selfridge Memorial Volume

%H <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-1).

%F For all elements x of the sequence, 15*x^2 + 10 is a square. Lim. n-> Inf. a(n)/a(n-1) = 4 + sqrt(15). - _Gregory V. Richardson_, Oct 13 2002

%F a(n) = 8*a(n-1)-a(n-2), a(-1)=-1, a(0)=1.

%F a(n) = S(n, 8)+S(n-1, 8) = S(2*n, sqrt(10)) with S(n, x) := U(n, x/2), Chebyshev polynomials of 2nd kind, A049310. S(n, 8) = A001090(n).

%F G.f.: (1+x)/(1-8*x+x^2).

%F a(n) = [ [(4+sqrt(15))^(n+1) - (4-sqrt(15))^(n+1)] + [(4+sqrt(15))^n - (4-sqrt(15))^n] ] / (2*sqrt(15)). - _Gregory V. Richardson_, Oct 13 2002

%F a(n) = sqrt((5*A070997(n)^2 - 2)/3) (cf. Richardson comment).

%F Let q(n, x) = sum(i=0, n, x^(n-i)*binomial(2*n-i, i)) then a(n) = (-1)^n*q(n,-10). - _Benoit Cloitre_, Nov 10 2002

%F a(n) = Jacobi_P(n,1/2,-1/2,4)/Jacobi_P(n,-1/2,1/2,1); - _Paul Barry_, Feb 03 2006

%F a(n+1) = 4*a(n)+((3*a(n)^2+2)*5)^0.5. - _Richard Choulet_, Aug 30 2007

%p A057080 := proc(n)

%p option remember;

%p if n <= 1 then

%p op(n+1,[1,9]);

%p else

%p 8*procname(n-1)-procname(n-2) ;

%p end if;

%p end proc: # _R. J. Mathar_, Apr 30 2017

%t CoefficientList[Series[(1 + x) / (1 - 8 x + x^2), {x, 0, 33}], x] (* _Vincenzo Librandi_, Mar 22 2015 *)

%o (Sage) [(lucas_number2(n,8,1)-lucas_number2(n-1,8,1))/6 for n in xrange(1, 21)] # _Zerinvary Lajos_, Nov 10 2009

%o (PARI) Vec((1+x)/(1-8*x+x^2) + O(x^30)) \\ _Michel Marcus_, Mar 22 2015

%o (MAGMA) I:=[1,9]; [n le 2 select I[n] else 8*Self(n-1)-Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Mar 22 2015

%Y Cf. A033890, A100047.

%K nonn,easy

%O 0,2

%A _Wolfdieter Lang_, Aug 04 2000

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Last modified November 17 08:39 EST 2019. Contains 329217 sequences. (Running on oeis4.)