A151610 Number of permutations of 7 indistinguishable copies of 1..n arranged in a circle with exactly 2 adjacent element pairs in decreasing order.

0, 252, 4935, 56560, 572215, 5503260, 51377823, 469758912, 4227854463, 37580958940, 330712475863, 2886218015856, 25013889523623, 215504279034492, 1847179534652655, 15762598695784192, 133982088914258095, 1134907106097349116, 9583660007044397799, 80704505322479268720

Offset

1,2

Links

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

Index entries for linear recurrences with constant coefficients, signature (19,-115,241,-208,64).

Formula

a(n) = n*((7/2)*8^n - 49*n) for n > 1. - Andrew Howroyd, May 04 2020

From Colin Barker, Jul 16 2020: (Start)

G.f.: 7*x^2*(36 + 21*x - 1175*x^2 + 624*x^3 - 192*x^4) / ((1 - x)^3*(1 - 8*x)^2).

a(n) = 19*a(n-1) - 115*a(n-2) + 241*a(n-3) - 208*a(n-4) + 64*a(n-5) for n>6.

(End)

Prog

(PARI) a(n) = if(n <= 1, 0, n*(7*8^n/2 - 49*n)) \\ Andrew Howroyd, May 04 2020
(PARI) concat(0, Vec(7*x^2*(36 + 21*x - 1175*x^2 + 624*x^3 - 192*x^4) / ((1 - x)^3*(1 - 8*x)^2) + O(x^20))) \\ Colin Barker, Jul 16 2020

Crossrefs

Cf. A151583.

Sequence in context: A184498 A169713 A099059 * A250085 A024018 A270853

Adjacent sequences: A151607 A151608 A151609 * A151611 A151612 A151613

Keyword

nonn,easy

Author

R. H. Hardin, May 21 2009

Extensions

Terms a(7) and beyond from Andrew Howroyd, May 04 2020

Status

approved