A026861 T(2n,n+1), T given by A026747.

1, 5, 22, 95, 411, 1790, 7855, 34725, 154573, 692450, 3120206, 14135555, 64356345, 294341325, 1351889910, 6233399525, 28845511125, 133933280000, 623811120960, 2913924782375, 13648296620445, 64087737455725, 301644762913977

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

a(n+1) = p(n+1) where p(x) is the unique degree-n polynomial such that p(k) = A002212(k+1) for k=0,1,...,n. - Michael Somos, Oct 07 2003

Number of skew Dyck paths of semilength n+1 containing at least one left step. - David Scambler, Jun 17 2013

Crossrefs

Cf. A000108, A002212, A026747.

Programs

PARI

a(n)=if(n<1,0,subst(polinterpolate(Vec((1-3*x-sqrt(1-6*x+5*x^2+x^2*O(x^n)))/2)),x,n+1))

Formula

a(n) = A002212(n+1) - A000108(n+1). - David Scambler, Jun 17 2013