A239117 Number of ballot sequences of length n with exactly 6 fixed points.

0, 0, 0, 0, 0, 0, 1, 1, 3, 9, 29, 99, 357, 1350, 5334, 21912, 93352, 410988, 1866492, 8720924, 41866020, 206085480, 1039120104, 5358418224, 28235017104, 151838491408, 832730775888, 4652886489840, 26470731088016, 153207256585824, 901628675631456, 5391563546317056

Offset: 0

Author

Joerg Arndt and Alois P. Heinz, Mar 10 2014

Keywords

• nonn
• easy

Comments

The fixed points are in the first 6 positions.

Also the number of standard Young tableaux with n cells such that the first column contains 1, 2, ..., 6, but not 7. An alternate definition uses the first row.

Examples

			a(6) = 1: [1,2,3,4,5,6].
a(7) = 1: [1,2,3,4,5,6,1].
a(8) = 3: [1,2,3,4,5,6,1,1], [1,2,3,4,5,6,1,2], [1,2,3,4,5,6,1,7].
a(9) = 9: [1,2,3,4,5,6,1,1,1], [1,2,3,4,5,6,1,1,2], [1,2,3,4,5,6,1,1,7], [1,2,3,4,5,6,1,2,1], [1,2,3,4,5,6,1,2,3], [1,2,3,4,5,6,1,2,7], [1,2,3,4,5,6,1,7,1], [1,2,3,4,5,6,1,7,2], [1,2,3,4,5,6,1,7,8].
		

Links

• Joerg Arndt and Alois P. Heinz, Table of n, a(n) for n = 0..800
• Wikipedia, Young tableau

Crossrefs

Column k=6 of A238802.

Programs

Maple

b:= proc(n) option remember; `if`(n<3, [1,1,3][n+1],
      ((114*n^3 -68193*n^2 +266129*n -764878)*b(n-1)
       +(2513*n^4 +25106*n^3 +330108*n^2 -382379*n +208440)*b(n-2)
       +(n-3)*(2399*n^3 +95128*n^2 +269793*n +65880)*b(n-3))/
       (2513*n^3+10142*n^2+201063*n-630958))
    end:
a:=n-> `if`(n<6, 0, b(n-6)):
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 == 6, 1, b[n - 7, {2, 1, 1, 1, 1, 1}]]; a[n_ /; n < 6] = 0; Table[ Print["a(", n, ") = ", an = a[n]]; an, {n, 0, 40}] (* Jean-François Alcover, Feb 06 2015, after Maple *)

Formula

See Maple program.

Recurrence (for n>=8): (n-7)*(n^6 - 28*n^5 + 350*n^4 - 3850*n^3 + 37569*n^2 - 201082*n + 556800)*a(n) = (n^7 - 35*n^6 + 441*n^5 - 3220*n^4 + 31444*n^3 - 314265*n^2 + 1921954*n - 5066880)*a(n-1) + (n-8)*(n-6)*(n^6 - 22*n^5 + 225*n^4 - 2710*n^3 + 27854*n^2 - 136228*n + 389760)*a(n-2). - Vaclav Kotesovec, Mar 11 2014

a(n) ~ sqrt(2)/1680 * exp(sqrt(n)-n/2-1/4) * n^(n/2) * (1+7/(24*sqrt(n))). - Vaclav Kotesovec, Mar 11 2014