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

5,1

Links

Table of n, a(n) for n=5..33.

Example

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.

Sequence in context: A362567 A074597 A350726 * A289399 A306093 A076207

Adjacent sequences: A241792 A241793 A241794 * A241796 A241797 A241798

Keyword

nonn

Author

Joerg Arndt and Alois P. Heinz, Apr 28 2014

Status

approved