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A026150 a(0) = a(1) = 1; a(n+2) = 2*a(n+1) + 2*a(n). 46
1, 1, 4, 10, 28, 76, 208, 568, 1552, 4240, 11584, 31648, 86464, 236224, 645376, 1763200, 4817152, 13160704, 35955712, 98232832, 268377088, 733219840, 2003193856, 5472827392, 14952042496, 40849739776 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n+1)/A002605(n) converges to sqrt(3). - Mario Catalani (mario.catalani(AT)unito.it), Apr 22 2003

a(n+1)/a(n) converges to 1+sqrt(3) = 2.732050807568877293.... - Philippe Deléham, Jul 03 2005

Binomial transform of expansion of cosh(sqrt(3)x) (A000244 with interpolated zeros); inverse binomial transform of A001075 . - Philippe Deléham, Jul 04 2005

The same sequence may be obtained by the following process. Starting a priori with the fraction 1/1, the numerators of fractions built according to the rule: add top and bottom to get the new bottom, add top and 3 times the bottom to get the new top. The limit of the sequence of fractions is sqrt(3). - Cino Hilliard, Sep 25 2005

Inverse binomial transform of A001075: (1, 2, 7, 26, 97, 362,...). - Gary W. Adamson, Nov 23 2007

Starting (1, 4, 10, 28, 76,...), the sequence is the binomial transform of [1, 3, 3, 9, 9, 27, 27, 81, 81,...], and inverse binomial transform of A001834: (1, 5, 19, 71, 265,...). - Gary W. Adamson, Nov 30 2007

[1,3; 1,1]^n * [1,0] = [A026150(n), A002605(n)]. - Gary W. Adamson, Mar 21 2008

(1+sqrt(3))^n = A026150(n) + A002605(n)*(sqrt(3)). - Gary W. Adamson, Mar 21 2008

Equals right border of triangle A143908. Also, starting (1, 4, 10, 28,...) = row sums of triangle A143908 and INVERT transform of (1, 3, 3, 3,...). - Gary W. Adamson, Sep 06 2008

a(n) is the number of compositions of n when there are 1 type of 1 and 3 types of other natural numbers. [Milan Janjic, Aug 13 2010]

An elephant sequence, see A175655. For the central square four A[5] vectors, with decimal values 85, 277, 337 and 340, lead to this sequence (without the first leading 1). For the corner squares these vectors lead to the companion sequence A002605 (without the leading 0). - Johannes W. Meijer, Aug 15 2010

Pisano period lengths: 1, 1, 1, 1, 24, 1, 48, 1, 3, 24, 10, 1, 12, 48, 24, 1,144, 3,180, 24,... - R. J. Mathar, Aug 10 2012

REFERENCES

John Derbyshire, Prime Obsession, Joseph Henry Press, April 2004, see p. 16.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..1000

Martin Burtscher, Igor Szczyrba, Rafał Szczyrba, Analytic Representations of the n-anacci Constants and Generalizations Thereof, Journal of Integer Sequences, Vol. 18 (2015), Article 15.4.5.

C. Banderier and D. Merlini, Lattice paths with an infinite set of jumps, FPSAC02, Melbourne, 2002.

C. Bautista-Ramos and C. Guillen-Galvan, Fibonacci numbers of generalized Zykov sums, J. Integer Seq., 15 (2012), Article 12.7.8.

A. Burstein, S. Kitaev and T. Mansour, Independent sets in certain classes of (almost) regular graphs

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1052

Tanya Khovanova, Recursive Sequences

Index entries for linear recurrences with constant coefficients, signature (2,2).

FORMULA

a(n) = (1/2)*((1+sqrt(3))^n+(1-sqrt(3))^n). - Benoit Cloitre, Oct 28 2002

G.f.: (1-x)/(1-2x-2x^2).

a(n) = a(n-1)+A083337(n-1). A083337(n)/a(n) converges to sqrt(3). - Mario Catalani (mario.catalani(AT)unito.it), Apr 29 2003

a(n) = sum{k=0..floor(n/2), C(n, 2k)3^k }; e.g.f.: exp(x)cosh(sqrt(3)x). - Paul Barry, May 15 2003

a(n) = Sum_{k, 0<=k<=n}A098158(n,k)*3^(n-k). - Philippe Deléham, Dec 26 2007

a(n) = upper left and lower right terms of [1,1; 3,1]^n. (1+sqrt(3))^n = a(n) + A083337(n)/(sqrt(3)). - Gary W. Adamson, Mar 12 2008

a(n) = A080040(n)/2. - Philippe Deléham, Nov 19 2008

If p[1]=1, and p[i]=3, (i>1), and if A is Hessenberg matrix of order n defined by: A[i,j]=p[j-i+1], (i<=j), A[i,j]=-1, (i=j+1), and A[i,j]=0 otherwise. Then, for n>=1, a(n)=det A. - Milan Janjic, Apr 29 2010

a(n) = 2 * A052945(n-1) - Vladimir Joseph Stephan Orlovsky, Mar 24 2011

a(n) = round((1+sqrt(3))^n/2) for n>0. - Bruno Berselli, Feb 04 2013

G.f.: G(0)/2, where G(k)= 1 + 1/(1 - x*(3*k-1)/(x*(3*k+2) - 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 25 2013

EXAMPLE

G.f. = 1 + x + 4*x^2 + 10*x^3 + 28*x^4 + 76*x^5 + 208*x^6 + 568*x^7 + ...

MAPLE

with(combstruct):ZL0:=S=Prod(Sequence(Prod(a, Sequence(b))), a):ZL1:=Prod(begin_blockP, Z, end_blockP):ZL2:=Prod(begin_blockLR, Z, Sequence(Prod(mu_length, Z), card>=1), end_blockLR): ZL3:=Prod(begin_blockRL, Sequence(Prod(mu_length, Z), card>=1), Z, end_blockRL):Q:=subs([a=Union(ZL2, ZL2, ZL2), b=ZL1], ZL0), begin_blockP=Epsilon, end_blockP=Epsilon, begin_blockLR=Epsilon, end_blockLR=Epsilon, begin_blockRL=Epsilon, end_blockRL=Epsilon, mu_length=Epsilon:temp15:=draw([S, {Q}, unlabelled], size=15):seq(count([S, {Q}, unlabelled], size=n)/3, n=2..27); # Zerinvary Lajos, Mar 08 2008

MATHEMATICA

Expand[Table[((1 + Sqrt[3])^n + (1 - Sqrt[3])^n)/(2), {n, 0, 30}]] (* Artur Jasinski, Dec 10 2006 *)

LinearRecurrence[{2, 2}, {1, 1}, 30] (* T. D. Noe, Mar 25 2011 *)

Round@Table[LucasL[n, Sqrt[2]] 2^(n/2 - 1), {n, 0, 20}] (* Vladimir Reshetnikov, Oct 15 2016 *)

PROG

(PARI) {a(n) = if( n<0, 0, real((1 + quadgen(12))^n))};

(Sage) from sage.combinat.sloane_functions import recur_gen2; it = recur_gen2(1, 1, 2, 2); [it.next() for i in range(30)] # Zerinvary Lajos, Jun 25 2008

(Sage) [lucas_number2(n, 2, -2)/2 for n in xrange(0, 26)] # Zerinvary Lajos, Apr 30 2009

(Haskell)

a026150 n = a026150_list !! n

a026150_list = 1 : 1 : map (* 2) (zipWith (+) a026150_list (tail

a026150_list))

-- Reinhard Zumkeller, Oct 15 2011

CROSSREFS

First differences of A002605.

The following sequences (and others) belong to the same family: A001333, A000129, A026150, A002605, A046717, A015518, A084057, A063727, A002533, A002532, A083098, A083099, A083100, A015519.

Cf. A001075, A001834, A083337, A002605, A143908, A028859, A030195, A106435, A108898, A125145.

Sequence in context: A203293 A111308 A121302 * A026123 A091468 A103457

Adjacent sequences:  A026147 A026148 A026149 * A026151 A026152 A026153

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified March 26 16:31 EDT 2017. Contains 284137 sequences.