G.f.: 1/(1-2x-15x^2)^(1/2); also, a(n) is the central coefficient of (1+x+4x^2)^n.

A084605

G.f.: 1/(1-2x-15x^2)^(1/2); also, a(n) is the central coefficient of (1+x+4x^2)^n.

Terms

    a(0) =1a(1) =1a(2) =9a(3) =25a(4) =145a(5) =561a(6) =2841a(7) =12489a(8) =60705a(9) =281185a(10) =1353769a(11) =6418809a(12) =30917041a(13) =148331665a(14) =716698425a(15) =3462260265a(16) =16786700865a(17) =81464917185a(18) =396215601225

External references