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

Author

Alois P. Heinz, Oct 19 2017

Keywords

• nonn

Links

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

Crossrefs

Column k=1 of A293881.

Programs

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);

Formula

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