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Search: id:A082631
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| A082631 |
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Enumeration of fractal 321 avoiders. |
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+0
1
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| 0, 1, 2, 6, 24, 116, 625, 3580, 21297, 130084, 810737, 5135142, 32961216, 213940962, 1401821021, 9260154974, 61603278951, 412352572116, 2775230479959, 18768654394542, 127482450424964, 869287197637752, 5948547336578541
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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See page 12-15 of link.
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LINKS
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M. H. Albert, The fine structure of 321 avoiding permutations.
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FORMULA
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G.f. A(x) satisfies A(x)^6+(-2*x+3)*A(x)^4+(-2*x-1)*A(x)^3+(x^2-3*x+3)*A(x)^2+(2*x^2-2*x-1)*A(x)+x^2+x=0; a(n+1)/a(n) ->7.346751...
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PROGRAM
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(PARI) a(n)=local(A); if(n<1, 0, A=x+O(x^2); for(m=2, n, A=Pol(A)+x*O(x^m); A=A^6+(-2*x+3)*A^4+(-2*x-1)*A^3+(x^2-3*x+3)*A^2+(2*x^2-2*x)*A+x^2+x); polcoeff(A, n))
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CROSSREFS
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Sequence in context: A068199 A128088 A069657 this_sequence A097483 A007405 A164871
Adjacent sequences: A082628 A082629 A082630 this_sequence A082632 A082633 A082634
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KEYWORD
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nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), May 24 2003
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