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A006497 a(n) = 3*a(n-1) + a(n-2).
(Formerly M0910)
19

%I M0910

%S 2,3,11,36,119,393,1298,4287,14159,46764,154451,510117,1684802,

%T 5564523,18378371,60699636,200477279,662131473,2186871698,7222746567,

%U 23855111399,78788080764,260219353691,859446141837,2838557779202

%N a(n) = 3*a(n-1) + a(n-2).

%C For more information about this type of recurrence follow the Khovanova link and see A086902 and A054413. - _Johannes W. Meijer_, Jun 12 2010

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Vincenzo Librandi, <a href="/A006497/b006497.txt">Table of n, a(n) for n = 0..1000</a>

%H P. Bhadouria, D. Jhala, B. Singh, <a href="http://www.tjmcs.com/includes/files/articles/Vol8_Iss1_81 - 92_Binomial_Transforms_of_the_k-Lucas.pdf">Binomial Transforms of the k-Lucas Sequences and its [sic] Properties</a>, The Journal of Mathematics and Computer Science (JMCS), Volume 8, Issue 1, Pages 81-92, Sequence L_{3,n}.

%H A. F. Horadam, <a href="http://www.fq.math.ca/Scanned/15-4/horadam.pdf">Generating identities for generalized Fibonacci and Lucas triples</a>, Fib. Quart., 15 (1977), 289-292.

%H Haruo Hosoya, <a href="http://www.hyle.org/journal/issues/19-1/hosoya.htm">What Can Mathematical Chemistry Contribute to the Development of Mathematics?</a>, HYLE--International Journal for Philosophy of Chemistry, Vol. 19, No.1 (2013), pp. 87-105.

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

%H Simon Plouffe, <a href="http://www.lacim.uqam.ca/%7Eplouffe/articles/MasterThesis.pdf">Approximations de séries génératrices et quelques conjectures</a>, Dissertation, Université du Québec à Montréal, 1992.

%H Simon Plouffe, <a href="http://www.lacim.uqam.ca/%7Eplouffe/articles/FonctionsGeneratrices.pdf">1031 Generating Functions and Conjectures</a>, Université du Québec à Montréal, 1992.

%H <a href="/index/Rea#recur1">Index entries for recurrences a(n) = k*a(n - 1) +/- a(n - 2)</a>

%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 (3,1).

%F G.f.: (2-3*x)/(1-3*x-x^2). - _Simon Plouffe_ in his 1992 dissertation

%F From _Gary W. Adamson_, Jun 15 2003: (Start)

%F a(n) = [(3 + sqrt13)/2]^n + [(3 - sqrt13)/2]^n.

%F A006190(n-2) + A006190(n) = a(n-1).

%F [a(n)]^2 - 13[A006190(n)]^2 = 4(-1)^n. (End)

%F From _Paul Barry_, Nov 15 2003: (Start)

%F E.g.f. : 2exp(3x/2)cosh(sqrt(13)x/2).

%F a(n) = 2^(1-n)*Sum_{k=0..floor(n/2)} C(n, 2*k)* (13)^k * 3^(n-2*k).

%F a(n) = 2*T(n, 3i/2)*(-i)^n with T(n, x) Chebyshev's polynomials of the first kind (see A053120) and i^2=-1. (End)

%F From _Hieronymus Fischer_, Jan 02 2009 (Start): fract(((3+sqrt(13))/2)^n))=(1/2)*(1+(-1)^n)-(-1)^n*((3+sqrt(13))/2)^(-n)=(1/2)*(1+(-1)^n)-((3-sqrt(13))/2)^n.

%F See A001622 for a general formula concerning the fractional parts of powers of numbers x>1, which satisfy x-x^(-1)=floor(x).

%F a(n) = round(((3+sqrt(13))/2)^n) for n>0. (End)

%F From _Johannes W. Meijer_, Jun 12 2010: (Start)

%F a(2n+1) = 3*A097783(n), a(2n) = A057076(n).

%F a(3n+1) = A041018(5n), a(3n+2) = A041018(5n+3) and a(3n+3) = 2*A041018(5n+4).

%F Limit(a(n+k)/a(k), k=infinity) = (a(n) + A006190(n)*sqrt(13))/2.

%F Limit(a(n)/A006190(n), n=infinity) = sqrt(13).

%F (End)

%F a(n) = sqrt(13*(A006190(n))^2 + 4*(-1)^n). - _Vladimir Shevelev_, Mar 13 2013

%F G.f.: G(0), where G(k)= 1 + 1/(1 - (x*(13*k-9))/((x*(13*k+4)) - 6/G(k+1))); (continued fraction). - _Sergei N. Gladkovskii_, Jun 15 2013

%F a(n) = [x^n] ( (1 + 3*x + sqrt(1 + 6*x + 13*x^2))/2 )^n for n >= 1. - _Peter Bala_, Jun 23 2015

%p a:= n-> (<<0|1>, <1|3>>^n. <<2, 3>>)[1, 1]:

%p seq(a(n), n=0..30); # _Alois P. Heinz_, Jan 26 2018

%t Table[LucasL[n, 3], {n, 0, 26}] (* _Zerinvary Lajos_, Jul 09 2009 *)

%o (Sage) [lucas_number2(n,3,-1) for n in xrange(0, 25)] # _Zerinvary Lajos_, Apr 30 2009

%o (MAGMA) [ n eq 1 select 2 else n eq 2 select 3 else 3*Self(n-1)+Self(n-2): n in [1..40] ]; // _Vincenzo Librandi_, Aug 20 2011

%o (Haskell)

%o a006497 n = a006497_list !! n

%o a006497_list = 2 : 3 : zipWith (+) (map (* 3) $ tail a006497_list) a006497_list

%o -- _Reinhard Zumkeller_, Feb 19 2011

%o (PARI) x='x+O('x^50); Vec((2-3*x)/(1-3*x-x^2)) \\ _G. C. Greubel_, Jul 05 2017

%Y Cf. A006190, A100230, A001622, A014176, A080039, A098316.

%K nonn,easy

%O 0,1

%A _N. J. A. Sloane_

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Last modified February 23 23:56 EST 2018. Contains 299595 sequences. (Running on oeis4.)