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A131313
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Number of labeled 4-arch graphs on n nodes.
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0
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OFFSET
| 1,6
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LINKS
| Saverio Caminiti and Emanuele G. Fusco, On the Number of Labeled k-arch Graphs, Journal of Integer Sequences, Vol 10 (2007), Article 07.7.5
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FORMULA
| The number of labeled 4-arch graps with n>5 nodes is given by f(n,4,n-4-1,0,4) where f is the recursive function described by the pari-gp code attached below.
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PROG
| (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
| Cf. A098721-A098724, A131311-A131315.
Sequence in context: A205602 A206162 A203409 * A129764 A027552 A098210
Adjacent sequences: A131310 A131311 A131312 * A131314 A131315 A131316
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KEYWORD
| nonn
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AUTHOR
| Saverio Caminiti and Emanuele G. Fusco (fusco(AT)di.uniroma1.it), Sep 18 2007
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Oct 02 2007
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