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A029698
Number of words of length 2n in the 10 transpositions of S[5] equivalent to the identity.
1
10, 340, 20860, 1770940, 169271260, 16731772540, 1668294277660, 166707356798140, 16667683919380060, 1666692097982207740, 166667302449546018460, 16666682561238613761340, 1666667064030965197232860, 166666676600774129343618940, 16666666915019353231241663260
OFFSET
1,1
LINKS
Justin Meiners, Computing the Rank of Braids, Master's Thesis, Brigham Young University (2021) 8947.
FORMULA
a(n) = (25*4^n+16*25^n +100^n)/60.
a(n) = 129*a(n-1)-3000*a(n-2)+10000*a(3). - Colin Barker, May 28 2015
G.f.: -10*x*(700*x^2-95*x+1) / ((4*x-1)*(25*x-1)*(100*x-1)). - Colin Barker, May 28 2015
MATHEMATICA
Rest@ CoefficientList[Series[-10 x (700 x^2 - 95 x + 1)/((4 x - 1)*(25 x - 1)*(100 x - 1)), {x, 0, 15}], x] (* Michael De Vlieger, Jul 06 2021 *)
PROG
(Magma) [(25*4^n+16*25^n +100^n)/60: n in [1..15]]; // Vincenzo Librandi, Jun 30 2011
(PARI) Vec(-10*x*(700*x^2-95*x+1) / ((4*x-1)*(25*x-1)*(100*x-1)) + O(x^100)) \\ Colin Barker, May 28 2015
CROSSREFS
Sequence in context: A046747 A338799 A006426 * A197598 A197982 A217506
KEYWORD
nonn,easy
AUTHOR
Paolo Dominici (pl.dm(AT)libero.it)
STATUS
approved