A027995 a(n) = Sum_{k=0..2n-1} T(n,k)*T(n,k+1), T given by A027926.

2, 9, 36, 140, 542, 2100, 8152, 31707, 123542, 482119, 1884060, 7371715, 28874778, 113213129, 444285136, 1744931000, 6858286418, 26974115244, 106157250796, 418025117820, 1646975313678, 6492134765114, 25602897974056, 101013355547390, 398698620627842, 1574259178022460

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Crossrefs

Cf. A027926.

Formula

G.f.: (-2*x+sqrt(1-4*x)-1)/(2*(x-1)*(sqrt(1-4*x)*x-4*x+1)). - Vladimir Kruchinin, Jul 20 2025