A159728 Number of permutations of 4 indistinguishable copies of 1..n arranged in a circle with exactly 2 local maxima.
36, 2610, 129800, 5748750, 241987500, 9885006250, 395426250000, 15570077343750, 605504070312500, 23311913238281250, 890091272109375000, 33749294301074218750, 1272088786561523437500, 47703329503967285156250, 1780924301526757812500000, 66228122463283630371093750
Offset: 2
Links
- Andrew Howroyd, Table of n, a(n) for n = 2..200
- Index entries for linear recurrences with constant coefficients, signature (85,-2350,23750,-100625,153125).
Programs
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PARI
a(n) = {2*n*(121*35^(n-2) + 8*5^(n-2) - 24*n*5^(n-2))/9} \\ Andrew Howroyd, May 10 2020 -
PARI
Vec(2*x^2*(3 + 5*x)*(6 - 85*x - 1100*x^2 + 875*x^3) / ((1 - 5*x)^3*(1 - 35*x)^2) + O(x^40)) \\ Colin Barker, Jul 16 2020
Formula
a(n) = 2*n*(121*35^(n-2) + 8*5^(n-2) - 24*n*5^(n-2))/9. - Andrew Howroyd, May 10 2020
Extensions
Terms a(8) and beyond from Andrew Howroyd, May 09 2020