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A151597 Number of permutations of 4 indistinguishable copies of 1..n arranged in a circle with exactly 2 adjacent element pairs in decreasing order. 2
0, 36, 606, 4744, 30850, 186924, 1092966, 6248976, 35154954, 195310900, 1074216814, 5859372696, 31738278546, 170898434364, 915527340150, 4882812495904, 25939941401626, 137329101557316, 724792480462974, 3814697265618600, 20027160644524194, 104904174804679756 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..500

Index entries for linear recurrences with constant coefficients, signature (13,-58,106,-85,25).

FORMULA

a(n) = n*(2*5^n - 16*n) for n > 1. - Andrew Howroyd, May 04 2020

From Colin Barker, Jul 16 2020: (Start)

G.f.: 2*x^2*(18 + 69*x - 523*x^2 + 255*x^3 - 75*x^4) / ((1 - x)^3*(1 - 5*x)^2).

a(n) = 13*a(n-1) - 58*a(n-2) + 106*a(n-3) - 85*a(n-4) + 25*a(n-5) for n>6.

(End)

PROG

(Magma) [0] cat [ n*(2*5^n - 16*n) : n in [2..30]]; // Wesley Ivan Hurt, Jul 16 2020

(PARI) a(n) = if(n <= 1, 0, n*(2*5^n - 16*n)) \\ Andrew Howroyd, May 04 2020

(PARI) concat(0, Vec(2*x^2*(18 + 69*x - 523*x^2 + 255*x^3 - 75*x^4) / ((1 - x)^3*(1 - 5*x)^2) + O(x^40))) \\ Colin Barker, Jul 16 2020

CROSSREFS

Cf. A151583.

Sequence in context: A003841 A226284 A223271 * A263957 A323974 A126926

Adjacent sequences: A151594 A151595 A151596 * A151598 A151599 A151600

KEYWORD

nonn,easy

AUTHOR

R. H. Hardin, May 21 2009

EXTENSIONS

Terms a(9) and beyond from Andrew Howroyd, May 04 2020

STATUS

approved

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Last modified December 8 08:56 EST 2022. Contains 358693 sequences. (Running on oeis4.)