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Search: id:A131312
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| A131312 |
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Number of labeled 3-arch graphs on n nodes. |
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+0
2
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| 0, 0, 1, 1, 10, 380, 34405, 5919536, 1709074584, 764754595200
(list; graph; listen)
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OFFSET
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1,5
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LINKS
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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
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The number of labeled 3-arch graps with n>4 nodes is given by f(n,3,n-3-1,0,3) where f is the recursive function described by the pari-gp code attached below.
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PROGRAM
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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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Cf. A098721-A098724, A131311-A131315.
Sequence in context: A117797 A117312 A000591 this_sequence A055733 A024136 A013405
Adjacent sequences: A131309 A131310 A131311 this_sequence A131313 A131314 A131315
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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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Edited by njas, Oct 02 2007
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