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A131314
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Number of labeled 5-arch graphs on n nodes.
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1
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0, 0, 0, 0, 1, 1, 21, 2576, 982926, 898027452, 1704360435624, 6105200593277808, 38418707658237401781, 401351360962291322915332, 6647604373581920953532817489, 168016310022000683846928851914752, 6273885184347679045743431356156590136
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OFFSET
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1,7
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LINKS
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FORMULA
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The number of labeled 5-arch graphs with n>6 nodes is given by f(n,5,n-5-1,0,5) where f is the recursive function described by the PARI/GP code below.
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PROG
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(PARI) f(n, k, i, u, j)={ local(s=0); if (i==1, binomial(n-u, j)*binomial(u, k-j), for (c=0, min(k, n-(i-1)-(u+j)), s+=f(n, k, i-1, u+j, c) ); binomial(n-u, j)*binomial(u, k-j)*s ) }
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Saverio Caminiti and Emanuele G. Fusco (fusco(AT)di.uniroma1.it), Sep 18 2007
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EXTENSIONS
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STATUS
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approved
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