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A152173
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a(n) is the number of Dyck paths of length n without height of peaks 1 (mod 3) and height of valleys 2 (mod 3)
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0
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1, 0, 1, 2, 4, 10, 23, 56, 138, 344, 870, 2220, 5716, 14828, 38717, 101682, 268416, 711810, 1895432, 5066030, 13586082, 36547534, 98593064, 266661162, 722953814, 1964358938, 5348367006, 14589803090, 39870312218, 109136843138
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,4
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REFERENCES
| Shu-Chung Liu, Jun Ma and Yeong-Nan Yeh, "Dyck Paths with Peak- and Valley-Avoiding Sets", Stud. Appl Math. 121 (3) (2008) 263-289
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FORMULA
| gf := (1-x-sqrt(1-2*x-3*x^2+4*x^4))/(2(1+x)x^2) ;
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CROSSREFS
| Cf. A127389. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 03 2008]
Sequence in context: A191693 A137681 A127389 * A032171 A127713 A151256
Adjacent sequences: A152170 A152171 A152172 * A152174 A152175 A152176
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KEYWORD
| nonn
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AUTHOR
| Jun Ma (majun(AT)math.sinica.edu.tw), Nov 27 2008
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