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Search: id:A112521
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| A112521 |
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Sequence related to NOR bracketings. |
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+0
1
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| 0, 1, 0, 6, 4, 60, 84, 700, 1440, 8910, 23100, 120120, 360360, 1684956, 5552064, 24302520, 85101456, 357502860, 1302562404, 5333981796, 19947127200, 80408748420, 305922388200, 1221485157360, 4701015343440, 18664243014300
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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Conjecture: Starting with n=1, a(n) is the main diagonal of the array defined as T(1,1) = 1, T(i,j) = 0 if i<1 or j<1, T(n,k) = T(n,k-2) + T(n,k-1) -2*T(n-1,k-1) + T(n-1,k) + T(n-2,k). [From Gerald McGarvey (gerald.mcgarvey(AT)comcast.net), Oct 07 2008]
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FORMULA
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a(n)=sum{j=0..n, (-1)^(n-1)*C(2n-j-1, n-j)*C(2(j-1), j-1)}; a(n)=n*A055392(n), n>1.
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CROSSREFS
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Sequence in context: A038258 A114330 A098657 this_sequence A109873 A014403 A077181
Adjacent sequences: A112518 A112519 A112520 this_sequence A112522 A112523 A112524
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Sep 09 2005
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