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A082631
Enumeration of fractal 321 avoiders.
0
0, 1, 2, 6, 24, 116, 625, 3580, 21297, 130084, 810737, 5135142, 32961216, 213940962, 1401821021, 9260154974, 61603278951, 412352572116, 2775230479959, 18768654394542, 127482450424964, 869287197637752, 5948547336578541
OFFSET
0,3
COMMENTS
See page 12-15 of link.
FORMULA
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...
PROG
(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))
CROSSREFS
Sequence in context: A211321 A242820 A228395 * A212198 A182216 A097483
KEYWORD
nonn
AUTHOR
Benoit Cloitre, May 24 2003
STATUS
approved