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A241795
Number of ballot sequences of length n having exactly two descents.
2
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
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
KEYWORD
nonn
AUTHOR
Joerg Arndt and Alois P. Heinz, Apr 28 2014
STATUS
approved