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 A027558 Number of 3-unbalanced strings of length n (= 2^n - A027557(n)). 1
 0, 0, 0, 0, 2, 6, 20, 50, 126, 288, 654, 1422, 3068, 6474, 13574, 28112, 57942, 118566, 241788, 490914, 994334, 2008512, 4050398, 8154014, 16396668, 32935194, 66104982, 132586416, 265792070, 532579830, 1066790972 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS a(n) is also the number of different ways to fold down a folding yardstick with n sticks (stick length is one) to form an equilateral tetragon (parallelogram) with side length one. - Frank Hollstein, May 01 2019 LINKS Table of n, a(n) for n=0..30. Index entries for linear recurrences with constant coefficients, signature (3,1,-8,2,4). FORMULA a(n) = 2*A005674(n). G.f.: -2*x^4/((2*x-1)*(2*x^2-1)*(x^2+x-1)). [Maksym Voznyy (voznyy(AT)mail.ru), Aug 12 2009] CROSSREFS Sequence in context: A121128 A056820 A204422 * A320910 A066397 A060344 Adjacent sequences: A027555 A027556 A027557 * A027559 A027560 A027561 KEYWORD nonn AUTHOR R. K. Guy, David Callan STATUS approved

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Last modified September 8 15:35 EDT 2024. Contains 375753 sequences. (Running on oeis4.)