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A029699 Number of words of length 4 in the n(n-1)/2 transpositions of S[ n ] equivalent to the identity. 1
0, 1, 27, 120, 340, 765, 1491, 2632, 4320, 6705, 9955, 14256, 19812, 26845, 35595, 46320, 59296, 74817, 93195, 114760, 139860, 168861, 202147, 240120, 283200, 331825, 386451, 447552, 515620, 591165, 674715, 766816, 868032, 978945, 1100155, 1232280, 1375956 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

FORMULA

a(n) = n*(n-1)*(3*n^2+n-12)/4.

a(n) = 5*a(n-1)-10*a(n-2)+10*a(n-3)-5*a(n-4)+a(n-5) for n>5. - Colin Barker, May 28 2015

G.f.: x^2*(5*x^2-22*x-1) / (x-1)^5. - Colin Barker, May 28 2015

PROG

(MAGMA) [n*(n-1)*(3*n^2+n-12)/4: n in [1..45]]; // Vincenzo Librandi, Jun 30 2011

(PARI) concat(0, Vec(x^2*(5*x^2-22*x-1) / (x-1)^5 + O(x^100))) \\ Colin Barker, May 28 2015

CROSSREFS

Sequence in context: A042428 A158554 A267812 * A087795 A036927 A232025

Adjacent sequences:  A029696 A029697 A029698 * A029700 A029701 A029702

KEYWORD

nonn,easy

AUTHOR

Paolo Dominici (pl.dm(AT)libero.it)

STATUS

approved

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Last modified November 19 22:34 EST 2019. Contains 329323 sequences. (Running on oeis4.)