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 A239118 Number of ballot sequences of length n with exactly 7 fixed points. 2
 0, 0, 0, 0, 0, 0, 0, 1, 1, 3, 9, 29, 99, 357, 1351, 5342, 21983, 93823, 414198, 1886424, 8846390, 42628782, 210773592, 1067599984, 5533263752, 29307314408, 158484944416, 874103230896, 4913196556800, 28120097476640, 163770757573776, 969858742317600 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,10 COMMENTS The fixed points are in the first 7 positions. Also the number of standard Young tableaux with n cells such that the first column contains 1, 2, ..., 7, but not 8.  An alternate definition uses the first row. LINKS Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 0..800 Wikipedia, Young tableau FORMULA See Maple program. Recurrence (for n>=9): (n-8)*(n^7 - 36*n^6 + 706*n^5 - 13080*n^4 + 177169*n^3 - 1264884*n^2 + 3776364*n - 9605520)*a(n) = (n^8 - 44*n^7 + 802*n^6 - 12104*n^5 + 206449*n^4 - 2516636*n^3 + 16735788*n^2 - 68051376*n + 170709120)*a(n-1) + (n-9)*(n-7)*(n^7 - 29*n^6 + 511*n^5 - 10055*n^4 + 131224*n^3 - 805316*n^2 + 1729104*n - 6929280)*a(n-2). - Vaclav Kotesovec, Mar 11 2014 a(n) ~ sqrt(2)/11520 * exp(sqrt(n)-n/2-1/4) * n^(n/2) * (1+7/(24*sqrt(n))). - Vaclav Kotesovec, Mar 11 2014 EXAMPLE a(7) = 1: [1,2,3,4,5,6,7]. a(8) = 1: [1,2,3,4,5,6,7,1]. a(9) = 3: [1,2,3,4,5,6,7,1,1], [1,2,3,4,5,6,7,1,2], [1,2,3,4,5,6,7,1,8]. a(10) = 9: [1,2,3,4,5,6,7,1,1,1], [1,2,3,4,5,6,7,1,1,2], [1,2,3,4,5,6,7,1,1,8], [1,2,3,4,5,6,7,1,2,1], [1,2,3,4,5,6,7,1,2,3], [1,2,3,4,5,6,7,1,2,8], [1,2,3,4,5,6,7,1,8,1], [1,2,3,4,5,6,7,1,8,2], [1,2,3,4,5,6,7,1,8,9]. MAPLE b:= proc(n) option remember; `if`(n<4, [1, 1, 3, 9][n+1],       ((41*n^2 +82925*n -562776)*b(n-1)        +(174*n^3 +63287*n^2 -447840*n +352440) *b(n-2)        +(133*n^3 -81472*n^2 +363510*n -267096) *b(n-3)        -(n-4)*(30661*n^2 -93002*n -90720) *b(n-4))/        (174*n^2+31449*n-246768))     end: a:=n-> `if`(n<7, 0, b(n-7)): seq(a(n), n=0..40); MATHEMATICA b[n_, l_List] := b[n, l] = If[n <= 0, 1, b[n - 1, Append[l, 1]] + Sum[If[i == 1 || l[[i - 1]] > l[[i]], b[n - 1, ReplacePart[l, i -> l[[i]] + 1]], 0], {i, 1, Length[l]}]]; a[n_] := If[n == 7, 1, b[n - 8, {2, 1, 1, 1, 1, 1, 1}]]; a[n_ /; n < 7] = 0; Table[ Print["a(", n, ") = ", an = a[n]]; an, {n, 0, 40}] (* Jean-François Alcover, Feb 06 2015, after Maple *) CROSSREFS Column k=7 of A238802. Sequence in context: A231291 A239116 A239117 * A239119 A238803 A148940 Adjacent sequences:  A239115 A239116 A239117 * A239119 A239120 A239121 KEYWORD nonn,easy AUTHOR Joerg Arndt and Alois P. Heinz, Mar 10 2014 STATUS approved

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Last modified June 15 19:35 EDT 2019. Contains 324144 sequences. (Running on oeis4.)