A217528 a(n) = (n-2)*(n-3)*2^(n-2)+2^n-2.

1, 2, 6, 22, 78, 254, 766, 2174, 5886, 15358, 38910, 96254, 233470, 557054, 1310718, 3047422, 7012350, 15990782, 36175870, 81264638, 181403646, 402653182, 889192446, 1954545662, 4278190078, 9328132094, 20266876926, 43889197054, 94757715966, 204010946558

Offset

1,2

Links

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

W. Griffiths, R. Smith and D. Warren, Almost avoiding pairs of permutations, PU. M. A. Vol. 22 (2011), 129-139.

Index entries for linear recurrences with constant coefficients, signature (7,-18,20,-8).

Formula

a(n) = 7*a(n-1)-18*a(n-2)+20*a(n-3)-8*a(n-4). G.f.: -x*(4*x^3-10*x^2+5*x-1)/((x-1)*(2*x-1)^3). [Colin Barker, Oct 17 2012]

Mathematica

Table[(n-2) (n-3) 2^(n-2) + 2^n - 2, {n, 30}] (* Vincenzo Librandi, Mar 11 2013 *)
LinearRecurrence[{7, -18, 20, -8}, {1, 2, 6, 22}, 30] (* Harvey P. Dale, Aug 08 2021 *)

Prog

(Maxima) makelist((n-2)*(n-3)*2^(n-2)+2^n-2, n, 1, 30); /* Martin Ettl, Oct 15 2012 */
(Magma) [(n-2)*(n-3)*2^(n-2)+2^n-2: n in [1..30]]; // Vincenzo Librandi, Mar 11 2013

Crossrefs

Sequence in context: A107239 A262068 A148496 * A181367 A106434 A150228

Adjacent sequences: A217525 A217526 A217527 * A217529 A217530 A217531

Keyword

nonn,easy

Author

N. J. A. Sloane, Oct 13 2012

Status

approved