A241795 Number of ballot sequences of length n having exactly two descents.

3, 21, 101, 373, 1174, 3337, 8642, 21148, 48713, 108147, 229984, 476430, 955667, 1879169, 3603751, 6801106, 12584048, 22974152, 41268291, 73301654, 128441712, 222871187, 382322022, 650209758, 1094918922, 1829777544, 3031447986, 4987910871, 8144753275

Offset: 5

Author

Joerg Arndt and Alois P. Heinz, Apr 28 2014

Keywords

• nonn

Examples

			a(5) = 3: [1,2,1,2,1], [1,2,1,3,1], [1,2,1,3,2].
		

Crossrefs

Column k=2 of A238121 and of A238122.