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 A130578 Number of different possible rows (or columns) in an n X n crossword puzzle. 14
 0, 0, 1, 3, 6, 10, 16, 26, 43, 71, 116, 188, 304, 492, 797, 1291, 2090, 3382, 5472, 8854, 14327, 23183, 37512, 60696, 98208, 158904, 257113, 416019, 673134, 1089154, 1762288, 2851442, 4613731, 7465175, 12078908, 19544084 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS The number of linear arrangements of n black and white squares subject to the conditions that there must be at least one run of white squares and all runs of white squares must be of length at least three. Crossword puzzles such as those in the New York Times do not include one-letter or two-letter words. Since the daily NYT puzzle is 15 X 15, there are a(15) = 797 different possible arrangements for each row. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..5000 Fumio Hazama, Spectra of graphs attached to the space of melodies, Discr. Math., 311 (2011), 2368-2383. See Table 2.1. Index entries for linear recurrences with constant coefficients, signature (3,-3,1,1,-1). FORMULA Recurrence: a[n + 4] = 2 a[n + 3] - a[n + 2] + a[n] + 1, with a[1] = 0, a[2] = 0, a[3] = 1, a[4] = 3. Formula: a[n] = (30 - 30*Sqrt[5] - 30*(1/2 - Sqrt[5]/2)^n + 12*Sqrt[5]*(1/2 - Sqrt[5]/2)^n + 15*(1/2 + Sqrt[5]/2)^n + 3*Sqrt[5]*(1/2 + Sqrt[5]/2)^n - 15*Cos[(n*Pi)/3] + 15*Sqrt[5]*Cos[(n*Pi)/3] + 5*Sqrt[3]*Sin[(n*Pi)/3] - 5*Sqrt[15]*Sin[(n*Pi)/3])/(30*(-1 + Sqrt[5]) O.g.f.: x^3/((-1+x)*(x^2+x-1)*(x^2-x+1)) . - R. J. Mathar, Nov 23 2007 a(n) = A005252(n+1) - 1. - R. J. Mathar, Nov 15 2011 G.f.: Q(0)*x^2/(2-2*x), where Q(k) = 1 + 1/(1 - x*( 4*k+2 -x +x^3)/( x*( 4*k+4 -x +x^3) +1/Q(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jan 07 2014 EXAMPLE a(5) = 6 because using 0's for white squares and 1's for black, the possible rows are: 00011, 10001, 11000, 00001, 10000, 00000. MATHEMATICA possiblerows = {}; For[n = 1, n <= 36, n++, table = Table[{n, k, Coefficient[(x^0 + Sum[x^i, {i, 3, n - k}])^(k + 1), x, n - k]}, {k, 0, n}]; total = Sum[table[[j, 3]], {j, 1, n}]; possiblerows = Append[possiblerows, total]; totalstable = Table[{t, possiblerows[[t]]}, {t, 1, Length[ possiblerows]}]]; TableForm[totalstable, TableHeadings -> {None, {" n = squares", "total number of permissible rows"}}] PROG (Haskell) a130578 n = a130578_list !! (n-1) a130578_list = 0 : 0 : 1 : 3 : zipWith (+)    (map (* 2) \$ drop 3 a130578_list)    (zipWith (-) (map (+ 1) a130578_list) (drop 2 a130578_list)) -- Reinhard Zumkeller, May 23 2013 (PARI) a(n)=([0, 1, 0, 0, 0; 0, 0, 1, 0, 0; 0, 0, 0, 1, 0; 0, 0, 0, 0, 1; -1, 1, 1, -3, 3]^n*[0; 0; 0; 1; 3])[1, 1] \\ Charles R Greathouse IV, Jun 11 2015 CROSSREFS Sequence in context: A265073 A265074 A054886 * A107068 A033541 A038505 Adjacent sequences:  A130575 A130576 A130577 * A130579 A130580 A130581 KEYWORD nonn,easy AUTHOR Marc A. Brodie (mbrodie(AT)wju.edu), Aug 10 2007, Aug 24 2007 STATUS approved

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Last modified September 27 18:56 EDT 2021. Contains 347694 sequences. (Running on oeis4.)