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A051449 Fibered rational knots with n crossings. 2
1, 1, 1, 2, 3, 4, 7, 10, 16, 25, 40, 62, 101, 159, 257, 410, 663, 1062, 1719, 2764, 4472, 7209, 11664, 18828, 30465, 49221, 79641, 128746, 208315, 336872, 545071, 881638, 1426520, 2307665, 3733880, 6040746, 9774133, 15813587, 25586921, 41398418 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,4

LINKS

Harvey P. Dale, Table of n, a(n) for n = 3..1000

Index entries for linear recurrences with constant coefficients, signature (0,2,2,1,-2,-2,-2,-1).

FORMULA

x^2/2*((-x-x^2)/(x^4+2x^3+x^2-1)+(-x-x^2)/(x^4+x^2-1)).

G.f. -x^3*(x^3+x-1)*(1+x)^2 / ( (1+x+x^2)*(x^2+x-1)*(x^4+x^2-1) )

EXAMPLE

a(7)=3 because there are 3 fibered rational knots with 7 crossings: 7_1, 7_6 and 7_7 (in Alexander-Briggs notation)

MATHEMATICA

f[x_] = -(x+1)^2*(x^3+x-1) / ((x^2+x-1)*(x^2+x+1)*(x^4+x^2-1)); CoefficientList[ Series[f[x], {x, 0, 39}], x]; Table[a[n], {n, 0, 20}](* Jean-Fran├žois Alcover, Nov 21 2011 *)

LinearRecurrence[{0, 2, 2, 1, -2, -2, -2, -1}, {1, 1, 1, 2, 3, 4, 7, 10}, 40] (* Harvey P. Dale, Dec 27 2015 *)

CROSSREFS

Sequence in context: A013982 A202411 A235648 * A018143 A281839 A136570

Adjacent sequences:  A051446 A051447 A051448 * A051450 A051451 A051452

KEYWORD

easy,nonn,nice

AUTHOR

Alexander Stoimenow (stoimeno(AT)math.toronto.edu)

EXTENSIONS

More terms from James A. Sellers

STATUS

approved

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Last modified September 26 10:43 EDT 2017. Contains 292518 sequences.