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1, 2, 2, 7, 14, 56, 132, 561, 1430, 6292, 16796, 75582, 208012, 950912, 2674440, 12369285, 35357670, 165002460, 477638700, 2244901890, 6564120420, 31030387440, 91482563640, 434542177290, 1289904147324, 6151850548776
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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Conjecture: n*(n-1)*(n-3)*(3*n-4)*a(n) -8*(n-1)*(2*n-5)*a(n-1) -4*(n-2)*(3*n-1)*(2*n-5)*(2*n-7)*a(n-2)=0. - R. J. Mathar, Jun 20 2015
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EXAMPLE
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a(4) = C(4) = 14.
a(5) = 56 = C(5) + C(4) = 42 + 14.
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PROG
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(Python)
from sympy import catalan
def a005807(n): return catalan(n) + catalan(n + 1)
def a048990(n): return catalan(2*n)
l=[1, 2]
for n in range(2, 31): l+=[a048990(n//2) if n%2==0 else a005807(n - 1)]
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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