

A001911


a(n) = Fibonacci(n+3)  2.
(Formerly M2546 N1007)


66



0, 1, 3, 6, 11, 19, 32, 53, 87, 142, 231, 375, 608, 985, 1595, 2582, 4179, 6763, 10944, 17709, 28655, 46366, 75023, 121391, 196416, 317809, 514227, 832038, 1346267, 2178307, 3524576, 5702885, 9227463, 14930350, 24157815, 39088167, 63245984
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OFFSET

0,3


COMMENTS

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
Ternary words of length n  1 with subwords (0, 1), (0, 2) and (2, 2) not allowed.  Olivier Gérard, Aug 28 2012
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, (711) 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
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 sumofproduct form in Equations (18) and (21) in our paper it follows that F(k+4)  2 = D(a(k+1))  D(b(k1)).  K.V.Iyer and P. Venkata Subba Reddy, Apr 30 2011
a(n) is the length of the nth palindromic prefix of the infinite Fibonacci word A003849.  Dimitri Hendriks, May 19 2014
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
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 (65=1, which is in {0, 1, 3, 6}), so it is added, resulting in 11.  Matthew Malone, Jan 03 2020


REFERENCES

J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 233.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 0..4783 (next term has 1001 digits)
Stefano Bilotta, Variablelength Nonoverlapping Codes, arXiv preprint arXiv:1605.03785 [cs.IT], 2016.
D. J. Broadhurst, On the enumeration of irreducible kfold Euler sums and their roles in knot theory and field theory, arXiv:hepth/9604128, 1996.
K. Viswanathan Iyer and K. R. Uday Kumar Reddy, Wiener index of binomial trees and Fibonacci trees, arXiv:0910.4432 [cs.DM], 2009. (Corrigendum: Eq.(23) to be corrected as follows on the rightside: 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).
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
M. Rigo, P. Salimov, and E. Vandomme, Some Properties of Abelian Return Words, Journal of Integer Sequences, Vol. 16 (2013), #13.2.5.
D. G. Rogers, An application of renewal sequences to the dimer problem, pp. 142153 of Combinatorial Mathematics VI (Armidale 1978), Lect. Notes Math. 748, 1979.
Wolfdieter Lang, Notes on certain inhomogeneous three term recurrences. [Wolfdieter Lang, Oct 17 2010]
Index entries for linear recurrences with constant coefficients, signature (2,0,1).


FORMULA

a(n) = a(n1) + a(n2) + 2, a(0) = 0, a(1) = 1.  Michael Somos, Jun 09 1999
G.f.: x*(1+x)/((1x)*(1xx^2)).
Sum of consecutive pairs of A000071 (partial sums of Fibonacci numbers).  Paul Barry, Apr 17 2004
a(n) = A101220(2, 1, n).  Ross La Haye, Jan 28 2005
a(n) = A108617(n+1, 2) = A108617(n+1, n1) for n > 0.  Reinhard Zumkeller, Jun 12 2005
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
a(0) = 0, a(1) = 1, a(2) = 3, a(n) = 2*a(n1)a(n3).  Harvey P. Dale, Jun 06 2011
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
a(n) = (2+(2^(n)*((1sqrt(5))^n*(2+sqrt(5))+(1+sqrt(5))^n*(2+sqrt(5))))/sqrt(5)).  Colin Barker, May 12 2016
a(n) = A000032(6+n)1 mod A000045(6+n).  Mario C. Enriquez, Apr 01 2017
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


EXAMPLE

x + 3*x^2 + 6*x^3 + 11*x^4 + 19*x^5 + 32*x^6 + 53*x^7 + 87*x^8 + ...


MAPLE

a[0]:=0:a[1]:=1:for n from 2 to 50 do a[n]:=a[n1]+a[n2]+2 od: seq(a[n], n=0..50); # Miklos Kristof, Mar 09 2005
A001911:=(1+z)/(z1)/(z**2+z1); # Simon Plouffe in his 1992 dissertation with another offset
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


MATHEMATICA

Table[Fibonacci[n + 3]  2, {n, 0, 5!}] (* Vladimir Joseph Stephan Orlovsky, Nov 19 2010 *)
LinearRecurrence[{2, 0, 1}, {0, 1, 3}, 40] (* Harvey P. Dale, Jun 06 2011 *)
Fibonacci[Range[3, 40]]2 (* Harvey P. Dale, Jun 28 2015 *)


PROG

(Magma) [(Fibonacci(n+3))2: n in [0..85]]; // Vincenzo Librandi, Apr 23 2011
(PARI) a(n)=fibonacci(n+3)2 \\ Charles R Greathouse IV, Mar 14 2012
(Haskell)
a001911 n = a001911_list !! n
a001911_list = 0 : 1 : map (+ 2) (zipWith (+) a001911_list $ tail a001911_list)
 Reinhard Zumkeller, Jun 18 2013


CROSSREFS

a(n) = A000045(n+3)  2.  Michael Somos, Jun 09 1999
Partial sums of F(n+1) = A000045(n+1).
Righthand column 3 of triangle A011794.
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]
Cf. A181631.  Gary W. Adamson, Nov 02 2010
See also A165910.
Subsequence of A226538.
Sequence in context: A183088 A326957 A116557 * A020957 A179006 A281573
Adjacent sequences: A001908 A001909 A001910 * A001912 A001913 A001914


KEYWORD

nonn,easy,nice


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms and better description from Michael Somos


STATUS

approved



