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 A048739 Expansion of 1/((1 - x)*(1 - 2*x - x^2)). 63
 1, 3, 8, 20, 49, 119, 288, 696, 1681, 4059, 9800, 23660, 57121, 137903, 332928, 803760, 1940449, 4684659, 11309768, 27304196, 65918161, 159140519, 384199200, 927538920, 2239277041, 5406093003, 13051463048, 31509019100, 76069501249 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Partial sums of Pell numbers A000129. W(n){1,3;2,-1,1} = Sum_{i=1..n} W(i){1,2;2,-1,0}, where W(n){a,b; p,q,r} implies x(n) = p*x(n-1) - q*x(n-2) + r; x(0)=a, x(1)=b. Number of 2 X (n+1) binary arrays with path of adjacent 1's from upper left to lower right corner. - R. H. Hardin, Mar 16 2002 Binomial transform of A029744. - Paul Barry, Apr 23 2004 Number of (s(0), s(1), ..., s(n+2)) such that 0 < s(i) < 4 and |s(i) - s(i-1)| <= 1 for i = 1,2,...,n+2, s(0) = 1, s(n+2) = 3. - Herbert Kociemba, Jun 16 2004 Equals row sums of triangle A153346. - Gary W. Adamson, Dec 24 2008 Equals the sum of the terms of the antidiagonals of A142978. - J. M. Bergot, Nov 13 2012 a(p-2) == 0 mod p where p is an odd prime, see A270342. - Altug Alkan, Mar 15 2016 Also, the lexicographically earliest sequence of positive integers such that for n > 3, {sqrt(2)*a(n)} is located strictly between {sqrt(2)*a(n-1)} and {sqrt(2)*a(n-2)} where {} denotes the fractional part. - Ivan Neretin, May 02 2017 a(n+1) is the number of weak orderings on {1,...,n} that are weakly single-peaked w.r.t. the total ordering 1 < ... < n. - J. Devillet, Oct 06 2017 REFERENCES Allombert, Bill, Nicolas Brisebarre, and Alain Lasjaunias. "On a two-valued sequence and related continued fractions in power series fields." The Ramanujan Journal 45.3 (2018): 859-871. See Theorem 3, d_{4n+3}. LINKS T. D. Noe, Table of n, a(n) for n = 0..200 M. Bicknell, A Primer on the Pell Sequence and related sequences, Fibonacci Quarterly, Vol. 13, No. 4, 1975, pp. 345-349. M. Bicknell-Johnson and G. E. Bergum, The Generalized Fibonacci Numbers {C(n)}, C(n)=C(n-1)+C(n-2)+K, Applications of Fibonacci Numbers, 1986, pp. 193-205. B. Bradie, Extensions and Refinements of some properties of sums involving Pell Numbers, Miss. J. Math. Sci 22 (1) (2010) 37-43 M. Couceiro, J. Devillet, and J.-L. Marichal, Quasitrivial semigroups: characterizations and enumerations, arXiv:1709.09162 [math.RA], 2017. Jimmy Devillet, On the single-peakedness property, International summer school "Preferences, decisions and games" (Sorbonne Université, Paris, 2019). I. M. Gessel, Ji Li, Compositions and Fibonacci identities, J. Int. Seq. 16 (2013) 13.4.5 A. F. Horadam, Special properties of the sequence W_n(a,b; p,q), Fib. Quart., 5.5 (1967), 424-434. INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1065 Yun-Tak Oh, Hosho Katsura, Hyun-Yong Lee, Jung Hoon Han, Proposal of a spin-one chain model with competing dimer and trimer interactions, arXiv:1709.01344 [cond-mat.str-el], 2017. Ahmet Öteleş, On the sum of Pell and Jacobsthal numbers by the determinants of Hessenberg matrices, AIP Conference Proceedings 1863, 310003 (2017). Index entries for linear recurrences with constant coefficients, signature (3,-1,-1) FORMULA a(n) = 2*a(n-1) + a(n-2) + 1 with n > 1, a(0)=1, a(1)=3. a(n) = ((2 + (3*sqrt(2))/2)*(1 + sqrt(2))^n - (2 - (3*sqrt(2))/2)*(1 - sqrt(2))^n )/(2*sqrt(2)) - 1/2. a(0)=1, a(n+1) = ceiling(x*a(n)) for n > 0, where x = 1+sqrt(2). - Paul D. Hanna, Apr 22 2003 a(n) = 3*a(n-1) - a(n-2) - a(n-3). With two leading zeros, e.g.f. is exp(x)(cosh(sqrt(2)x)-1)/2. a(n) = Sum_{k=0..floor((n+2)/2)} binomial(n+2, 2k+2)2^k. - Paul Barry, Aug 16 2003 -a(-3-n) = A077921(n). - N. J. A. Sloane, Sep 13 2003 E.g.f.: exp(x)(cosh(x/sqrt(2)) + sqrt(2)sinh(x/sqrt(2)))^2. - N. J. A. Sloane, Sep 13 2003 a(n) = floor((1+sqrt(2))^(n+2)/4). - Bruno Berselli, Feb 06 2013 a(n) = (((1-sqrt(2))^(n+2) + (1+sqrt(2))^(n+2) - 2) / 4). - Altug Alkan, Mar 16 2016 2*a(n) = A001333(n+2)-1. - R. J. Mathar, Oct 11 2017 a(n) = Sum_{k=0..n} binomial(n+1,k+1)*2^floor(k/2). - Tony Foster III, Oct 12 2017 MAPLE a:=n->sum(fibonacci(i, 2), i=0..n): seq(a(n), n=1..29); # Zerinvary Lajos, Mar 20 2008 MATHEMATICA Join[{a=1, b=3}, Table[c=2*b+a+1; a=b; b=c, {n, 60}]] (* Vladimir Joseph Stephan Orlovsky, Feb 01 2011 *) CoefficientList[Series[1/(1-3x+x^2+x^3), {x, 0, 30}], x] (* or *) LinearRecurrence[{3, -1, -1}, {1, 3, 8}, 30] (* Harvey P. Dale, Jun 13 2011 *) PROG (PARI) a(n)=local(w=quadgen(8)); -1/2+(3/4+1/2*w)*(1+w)^n+(3/4-1/2*w)*(1-w)^n (PARI) vector(100, n, n--; floor((1+sqrt(2))^(n+2)/4)) \\ Altug Alkan, Oct 07 2015 (PARI) Vec(1/((1-x)*(1-2*x-x^2)) + O(x^40)) \\ Michel Marcus, May 06 2017 CROSSREFS First row of table A083087. With a different offset, a(4n)=A008843(n), a(4n-2)=8*A001110(n), a(2n-1)=A001652(n). Cf. A001333, A048654, A048655, A083044, A083047, A083050, A153346. Sequence in context: A038746 A126876 A090757 * A054192 A124523 A054185 Adjacent sequences:  A048736 A048737 A048738 * A048740 A048741 A048742 KEYWORD easy,nice,nonn,changed AUTHOR EXTENSIONS Corrected and extended by Larry Reeves (larryr(AT)acm.org), Jun 11 2002 STATUS approved

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Last modified November 19 03:48 EST 2019. Contains 329310 sequences. (Running on oeis4.)