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A288679
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Number of Dyck paths of semilength n such that no positive level has fewer than three peaks.
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2
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1, 0, 0, 1, 1, 1, 1, 5, 30, 96, 245, 592, 1543, 4884, 17660, 64495, 226442, 766937, 2558655, 8590293, 29408344, 102893203, 366035420, 1314955687, 4747101946, 17184305311, 62359953380, 226978626707, 829122987011, 3040369502702, 11191473790567, 41342469523031
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OFFSET
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0,8
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LINKS
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MATHEMATICA
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b[n_, k_, j_]:=b[n, k, j]=If[j==n, 1, Sum[Sum[Binomial[i, m] Binomial[j - 1, i - 1 - m], {m, Max[k, i - j], i - 1}] b[n - j, k, i], {i, n - j}]]; a[n_]:=If[n==0, 1, Sum[b[n, 3, j], {j, 3, n}]]; Table[a[n], {n, 0, 35}] (* Indranil Ghosh, Aug 09 2017 *)
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PROG
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(Python)
from sympy.core.cache import cacheit
from sympy import binomial
@cacheit
def b(n, k, j): return 1 if j==n else sum([sum([binomial(i, m)*binomial(j - 1, i - 1 - m) for m in range(max(k, i - j), i)])*b(n - j, k, i) for i in range(1, n - j + 1)])
def a(n): return 1 if n==0 else sum([b(n, 3, j) for j in range(3, n + 1)])
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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