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 A006355 Number of binary vectors of length n containing no singletons. 82
 1, 0, 2, 2, 4, 6, 10, 16, 26, 42, 68, 110, 178, 288, 466, 754, 1220, 1974, 3194, 5168, 8362, 13530, 21892, 35422, 57314, 92736, 150050, 242786, 392836, 635622, 1028458, 1664080, 2692538, 4356618, 7049156, 11405774, 18454930, 29860704, 48315634 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Number of cvtemplates at n-2 letters given <= 2 consecutive consonants or vowels (n >= 4). Number of (n,2) Freiman-Wyner sequences. Diagonal sums of the Riordan array ((1-x+x^2)/(1-x), x/(1-x)), A072405 (where this begins 1,0,1,1,1,1,...). - Paul Barry, May 04 2005 a(n) = A119457(n-1,n-2) for n > 2. - Reinhard Zumkeller, May 20 2006 Central terms of the triangle in A094570. - Reinhard Zumkeller, Mar 22 2011 Pisano period lengths: 1, 1, 8, 3, 20, 8, 16, 6, 24, 20, 10, 24, 28, 16, 40, 12, 36, 24, 18, 60, ... . - R. J. Mathar, Aug 10 2012 Also the number of matchings in the (n-2)-pan graph for n >= 5. - Eric W. Weisstein, Oct 03 2017 REFERENCES A. T. Benjamin and J. J. Quinn, Proofs that really count: the art of combinatorial proof, M.A.A. 2003, id. 16, 51. Noriaki Sannomiya, H Katsura, Y Nakayama, Supersymmetry breaking and Nambu-Goldstone fermions with cubic dispersion, arXiv preprint arXiv:1612.02285, 2016. See Table II, line 2. LINKS Charles R Greathouse IV, Table of n, a(n) for n = 0..4786 (next term has 1001 digits) J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy] Ian F. Blake, The enumeration of certain run length sequences, Information and Control, 55 (1982), 222-237. A. Burstein, S. Kitaev, T. Mansour, Partially ordered patterns and their combinatorial interpretations, PU. M. A. Vol. 19 (2008), No. 2-3, pp. 27-38. Enoch Haga, Room for Expansion, Word Ways, 33 (No. 2, 2000), pp. 106-113 (see p. 110). INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 898. Sergey Kitaev, Jeffrey Remmel, (a,b)-rectangle patterns in permutations and words, arXiv:1304.4286 [math.CO], 2013. Eric Weisstein's World of Mathematics, Independent Edge Set, Matching and Pan Graph. Index entries for linear recurrences with constant coefficients, signature (1,1). FORMULA a(n+2) = F(n-1) + F(n+2), for n > 0. G.f.: (1-x+x^2)/(1-x-x^2). - Paul Barry, May 04 2005 a(n) = 2*F(n-1) for n > 0, F(n)=A000045(n) and a(0)=1. - Mircea Merca, Jun 28 2012 G.f.: 1 - x + x*Q(0), where Q(k) = 1 + x^2 + (2*k+3)*x - x*(2*k+1 + x)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Oct 05 2013 a(n) = A118658(n) - 0^n. - M. F. Hasler, Nov 05 2014 a(n) = (2^(-n)*((1-r)^n*(1+r) + (-1+r)*(1+r)^n)) / r for n > 0, where r=sqrt(5). - Colin Barker, Jan 28 2017 EXAMPLE a(6)=10 because we have: 000000, 000011, 000111, 001100, 001111, 110000, 110011, 111000, 111100, 111111. - Geoffrey Critzer, Jan 26 2014 MAPLE a:= n-> if n=0 then 1 else (Matrix([[2, -2]]). Matrix([[1, 1], [1, 0]])^n) [1, 1] fi: seq(a(n), n=0..38); # Alois P. Heinz, Aug 18 2008 MATHEMATICA Join[{1}, Last[#] - First[#] & /@ Partition[Fibonacci[Range[-1, 40]], 4, 1]] (* Harvey P. Dale, Sep 30 2011 *) Join[{1}, LinearRecurrence[{1, 1}, {0, 2}, 38]] (* Jean-François Alcover, Sep 23 2017 *) Join[{1}, Table[2 Fibonacci[n], {n, 0, 20}]] (* Eric W. Weisstein, Oct 03 2017 *) Join[{1}, 2 Fibonacci[Range[0, 20]]] (* Eric W. Weisstein, Oct 03 2017 *) CoefficientList[Series[(-1 + x - x^2)/(-1 + x + x^2), {x, 0, 20}], x] (* Eric W. Weisstein, Oct 03 2017 *) PROG (PARI) a(n)=if(n, 2*fibonacci(n-1), 1) \\ Charles R Greathouse IV, Mar 14 2012 (Haskell) a006355 n = a006355_list !! n a006355_list = 1 : fib2s where    fib2s = 0 : map (+ 1) (scanl (+) 1 fib2s) -- Reinhard Zumkeller, Mar 20 2013 (MAGMA) [1] cat [Lucas(n) - Fibonacci(n): n in [1..50]]; // Vincenzo Librandi, Aug 02 2014 (PARI) x='x+O('x^50); Vec((1-x+x^2)/(1-x-x^2)) \\ Altug Alkan, Nov 01 2015 CROSSREFS Except for initial term, = 2*Fibonacci numbers (A000045). Essentially the same as A047992, A054886 A055389, A068922, and A090991. Cf. A097925, A097926. Column 2 in A265584. Sequence in context: A228807 A262258 A293633 * A055389 A163733 A198834 Adjacent sequences:  A006352 A006353 A006354 * A006356 A006357 A006358 KEYWORD nonn,easy,nice AUTHOR David M. Bloom EXTENSIONS More terms from Reinhard Zumkeller, May 20 2006 Corrected by T. D. Noe, Oct 31 2006 STATUS approved

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