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A124280
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Expansion of 1/(1-x-x^2+x^3-x^4).
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2
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1, 1, 2, 2, 4, 5, 9, 12, 20, 28, 45, 65, 102, 150, 232, 345, 529, 792, 1208, 1816, 2761, 4161, 6314, 9530, 14444, 21821, 33049, 49956, 75628, 114356, 173077, 261761, 396110, 599150, 906576, 1371377, 2074913, 3138864
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OFFSET
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0,3
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COMMENTS
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Diagonal sums of number triangle A124279.
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LINKS
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FORMULA
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a(n) = sum{k=0..floor(n/2), sum{j=0..n-2k, C(j,n-2k-j)C(k,n-2k-j)}}.
a(n) = a(n-1)+a(n-2)-a(n-3)+a(n-4), a(0)=1, a(1)=1, a(2)=2, a(3)=2. - Carl Najafi, May 06 2014
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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