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1, 2, 13, 180, 3844, 110908, 4030740, 176640072, 9059743648, 532179428700, 35219852623888, 2592514449263656, 210072673380786552, 18579938909696752728, 1780987027765227959096, 183907984490301947455872
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} C(k^2, k) * C((n-k)^2, n-k).
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PROG
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(PARI) a(n)=sum(k=0, n, binomial(k^2, k)*binomial((n-k)^2, n-k))
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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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