cp's OEIS Frontend

A001911 a(n) = Fibonacci(n+3) - 2.

%I A001911 M2546 N1007 #181 Jun 30 2025 21:12:00
%S A001911 0,1,3,6,11,19,32,53,87,142,231,375,608,985,1595,2582,4179,6763,10944,
%T A001911 17709,28655,46366,75023,121391,196416,317809,514227,832038,1346267,
%U A001911 2178307,3524576,5702885,9227463,14930350,24157815,39088167,63245984
%N A001911 a(n) = Fibonacci(n+3) - 2.
%C A001911 This is the sequence A(0,1;1,1;2) of the family of sequences [a,b:c,d:k] considered by G. Detlefs, and treated as A(a,b;c,d;k) in the W. Lang link given below. - _Wolfdieter Lang_, Oct 17 2010
%C A001911 Ternary words of length n - 1 with subwords (0, 1), (0, 2) and (2, 2) not allowed. - _Olivier Gérard_, Aug 28 2012
%C A001911 For subsets of (1, 2, 3, 5, 8, 13, ...) Fibonacci Maximal terms (Cf. A181631) equals the number of leading 1's per subset. For example, (7-11) in Fibonacci Maximal = (1010, 1011, 1101, 1110, 1111), numbers of leading 1's = (1 + 1 + 2 + 3 + 4) = 11 = a(4) = row 4 of triangle A181631. - _Gary W. Adamson_, Nov 02 2010
%C A001911 As in our 2009 paper, we use two types of Fibonacci trees: - Ta: Fibonacci analog of binomial trees; Tb: Binary Fibonacci trees. Let D(r(k)) be the sum over all distances of the form d(r, x), across all vertices x of the tree rooted at r of order k. Ignoring r, but overloading, let D(a(k)) and D(b(k)) be the distance sums for the Fibonacci trees Ta and Tb respectively of the order k. Using the sum-of-product form in Equations (18) and (21) in our paper it follows that F(k+4) - 2 = D(a(k+1)) - D(b(k-1)). - _K.V.Iyer_ and P. Venkata Subba Reddy, Apr 30 2011
%C A001911 a(n) is the length of the n-th palindromic prefix of the infinite Fibonacci word A003849. - _Dimitri Hendriks_, May 19 2014
%C A001911 The first k terms of the infinite Fibonacci word A014675 are palindromic if and only if k is a positive term of this sequence. - _Clark Kimberling_, Jul 14 2014
%C A001911 Can be expressed in terms of a rule similar to Recamán's sequence (A005132). Instead of following the Recamán rule "subtract if possible, otherwise add", this sequence follows the rule "If subtraction is possible, do nothing; otherwise add." For example when at the fourth term, 6, it is possible to subtract 4 (giving 2 which is not in {0, 1, 3, 6}) so nothing is done with 4. It is not possible to subtract 5 (6-5=1, which is in {0, 1, 3, 6}), so it is added, resulting in 11. - _Matthew Malone_, Jan 03 2020
%C A001911 For n>=1, a(n) is the maximum number of vertices (Moore bound) of a (1,1)-regular mixed graph with diameter n-1. - _Miquel A. Fiol_, Jun 24 2024
%C A001911 Repunits in the lazy Fibonacci representation (A104326), and which is the first row of array A372501. - _A.H.M. Smeets_, Jun 25 2025
%D A001911 J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 233.
%D A001911 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A001911 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A001911 Charles R Greathouse IV, <a href="/A001911/b001911.txt">Table of n, a(n) for n = 0..4783</a> (next term has 1001 digits)
%H A001911 Stefano Bilotta, <a href="http://arxiv.org/abs/1605.03785">Variable-length Non-overlapping Codes</a>, arXiv preprint arXiv:1605.03785 [cs.IT], 2016.
%H A001911 D. J. Broadhurst, <a href="http://arXiv.org/abs/hep-th/9604128">On the enumeration of irreducible k-fold Euler sums and their roles in knot theory and field theory</a>, arXiv:hep-th/9604128, 1996.
%H A001911 C. Dalfó, G. Erskine, G. Exoo, M. A. Fiol, N. López, A. Messegué, and J. Tuite, <a href="https://doi.org/10.1016/j.dam.2024.06.001">On large regular (1,1,k)-mixed graphs</a>, Discrete Appl. Math. 356 (2024), 209-228.
%H A001911 Ricardo Gómez Aíza, <a href="https://arxiv.org/abs/2402.16111">Trees with flowers: A catalog of integer partition and integer composition trees with their asymptotic analysis</a>, arXiv:2402.16111 [math.CO], 2024. See p. 23.
%H A001911 K. Viswanathan Iyer and K. R. Uday Kumar Reddy, <a href="http://arXiv.org/abs/0910.4432">Wiener index of binomial trees and Fibonacci trees</a>, arXiv:0910.4432 [cs.DM], 2009. (Corrigendum: Eq.(23) to be corrected as follows on the right-side: in the fourth term F(k)-1 should be replaced by F(k); a term F(k)*F(K+1)-1 is to be included; pointed out by Emeric Deutsch).
%H A001911 Simon Plouffe, <a href="https://arxiv.org/abs/0911.4975">Approximations de séries génératrices et quelques conjectures</a>, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
%H A001911 Simon Plouffe, <a href="/A000051/a000051_2.pdf">1031 Generating Functions</a>, Appendix to Thesis, Montreal, 1992
%H A001911 M. Rigo, P. Salimov, and E. Vandomme, <a href="http://www.emis.de/journals/JIS/VOL16/Rigo/rigo3.html">Some Properties of Abelian Return Words</a>, Journal of Integer Sequences, Vol. 16 (2013), #13.2.5.
%H A001911 D. G. Rogers, <a href="http://dx.doi.org/10.1007/BFb0102693">An application of renewal sequences to the dimer problem</a>, pp. 142-153 of Combinatorial Mathematics VI (Armidale 1978), Lect. Notes Math. 748, 1979.
%H A001911 Wolfdieter Lang, <a href="/A001911/a001911.pdf">Notes on certain inhomogeneous three term recurrences</a>, 2010.
%H A001911 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-1).
%F A001911 From _Michael Somos_, Jun 09 1999: (Start)
%F A001911 a(n) = A000045(n+3) - 2.
%F A001911 a(n) = a(n-1) + a(n-2) + 2, a(0) = 0, a(1) = 1. (End)
%F A001911 G.f.: x*(1+x)/((1-x)*(1-x-x^2)).
%F A001911 Sum of consecutive pairs of A000071 (partial sums of Fibonacci numbers). - _Paul Barry_, Apr 17 2004
%F A001911 a(n) = A101220(2, 1, n). - _Ross La Haye_, Jan 28 2005
%F A001911 a(n) = A108617(n+1, 2) = A108617(n+1, n-1) for n > 0. - _Reinhard Zumkeller_, Jun 12 2005
%F A001911 a(n) = term (1,1) in the 1 X 3 matrix [0,-1,1].[1,1,0; 1,0,0; 2,0,1]^n. - _Alois P. Heinz_, Jul 24 2008
%F A001911 a(0) = 0, a(1) = 1, a(2) = 3, a(n) = 2*a(n-1)-a(n-3). - _Harvey P. Dale_, Jun 06 2011
%F A001911 Eigensequence of an infinite lower triangular matrix with the natural numbers as the left border and (1, 0, 1, 0, ...) in all other columns. - _Gary W. Adamson_, Jan 30 2012
%F A001911 a(n) = (-2+(2^(-n)*((1-sqrt(5))^n*(-2+sqrt(5))+(1+sqrt(5))^n*(2+sqrt(5))))/sqrt(5)). - _Colin Barker_, May 12 2016
%F A001911 a(n) = A000032(6+n)-1 mod A000045(6+n). - _Mario C. Enriquez_, Apr 01 2017
%F A001911 E.g.f.: 2*exp(x/2)*(5*cosh(sqrt(5)*x/2) + 2*sqrt(5)*sinh(sqrt(5)*x/2))/5 - 2*exp(x). - _Stefano Spezia_, May 08 2022
%e A001911 G.f. = x + 3*x^2 + 6*x^3 + 11*x^4 + 19*x^5 + 32*x^6 + 53*x^7 + 87*x^8 + ...
%p A001911 a[0]:=0:a[1]:=1:for n from 2 to 50 do a[n]:=a[n-1]+a[n-2]+2 od: seq(a[n],n=0..50); # _Miklos Kristof_, Mar 09 2005
%p A001911 A001911:=(1+z)/(z-1)/(z**2+z-1); # _Simon Plouffe_ in his 1992 dissertation with another offset
%p A001911 a:= n-> (Matrix([[0,-1,1]]). Matrix([[1,1,0], [1,0,0], [2,0,1]])^n)[1,1]: seq(a(n), n=0..50); # _Alois P. Heinz_, Jul 24 2008
%t A001911 Table[Fibonacci[n+3] -2, {n,0,50}] (* _Vladimir Joseph Stephan Orlovsky_, Nov 19 2010 *)
%t A001911 LinearRecurrence[{2,0,-1}, {0,1,3}, 40] (* _Harvey P. Dale_, Jun 06 2011 *)
%t A001911 Fibonacci[Range[3,40]]-2 (* _Harvey P. Dale_, Jun 28 2015 *)
%o A001911 (Magma) [(Fibonacci(n+3))-2: n in [0..85]]; // _Vincenzo Librandi_, Apr 23 2011
%o A001911 (PARI) a(n)=fibonacci(n+3)-2 \\ _Charles R Greathouse IV_, Mar 14 2012
%o A001911 (Haskell)
%o A001911 a001911 n = a001911_list !! n
%o A001911 a001911_list = 0 : 1 : map (+ 2) (zipWith (+) a001911_list $ tail a001911_list)
%o A001911 -- _Reinhard Zumkeller_, Jun 18 2013
%o A001911 (SageMath) [fibonacci(n+3)-2 for n in range(60)] # _G. C. Greubel_, Oct 21 2024
%Y A001911 Cf. A000032, A000045, A101220, A104326, A108617, A181631, A372501.
%Y A001911 Cf. A001611, A000071, A157725, A001911, A157726, A006327, A157727, A157728, A157729, A167616. [Added by _N. J. A. Sloane_, Jun 25 2010 in response to a comment from _Aviezri S. Fraenkel_]
%Y A001911 Partial sums of A000045(n+1).
%Y A001911 Right-hand column 3 of triangle A011794.
%Y A001911 See also A165910.
%Y A001911 Subsequence of A226538.
%Y A001911 Column k=3 of A261019.
%K A001911 nonn,easy,nice
%O A001911 0,3
%A A001911 _N. J. A. Sloane_
%E A001911 More terms and better description from _Michael Somos_