A293914 Number of linear chord diagrams having n chords and minimal chord length one.

1, 2, 10, 69, 616, 6740, 87291, 1305710, 22149226, 420113979, 8810083360, 202397302184, 5054993327385, 136370982998354, 3951907646699026, 122432049983991285, 4038019273764782056, 141261207847788852620, 5224370049771189478371, 203670050053447478737214

Offset

1,2

Links

Alois P. Heinz, Table of n, a(n) for n = 1..404

Formula

a(n) ~ (1 - exp(-1)) * 2^(n + 1/2) * n^n / exp(n). - Vaclav Kotesovec, Oct 25 2017

Maple

a:= proc(n) option remember; `if`(n<3, n, (4*n-6)*
      a(n-1)-2*(2*n^2-8*n+7)*a(n-2)-(2*n-5)*a(n-3))
    end:
seq(a(n), n=1..25);

Crossrefs

Column k=1 of A293881.

Sequence in context: A123617 A325054 A139715 * A259114 A051575 A372940

Adjacent sequences: A293911 A293912 A293913 * A293915 A293916 A293917

Keyword

nonn

Author

Alois P. Heinz, Oct 19 2017

Status

approved