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A029697
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Number of words of length 2n in the 6 transpositions of S[ 4 ] equivalent to the identity.
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1
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6, 120, 3936, 140160, 5039616, 181401600, 6530359296, 235092541440, 8463329918976, 304679870791680, 10968475323334656, 394865111539384320, 14215144015015182336, 511745184538935951360, 18422826643395251798016, 663221759162203294924800
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OFFSET
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1,1
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..300
Index entries for linear recurrences with constant coefficients, signature (40,-144).
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FORMULA
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a(n) = (9*4^n+36^n)/12.
a(n) = 40*a(n-1)-144*a(n-2). - Colin Barker, May 28 2015
G.f.: -6*x*(20*x-1) / ((4*x-1)*(36*x-1)). - Colin Barker, May 28 2015
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PROG
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(MAGMA) [(9*4^n+36^n)/12: n in [1..15]]; // Vincenzo Librandi, Jun 30 2011
(PARI) Vec(-6*x*(20*x-1) / ((4*x-1)*(36*x-1)) + O(x^100)) \\ Colin Barker, May 28 2015
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CROSSREFS
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Sequence in context: A246611 A185757 A075844 * A248045 A280627 A196688
Adjacent sequences: A029694 A029695 A029696 * A029698 A029699 A029700
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KEYWORD
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nonn,easy
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AUTHOR
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Paolo Dominici (pl.dm(AT)libero.it)
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STATUS
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approved
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