A217529 a(n) = 2^(n-4)*(4*n^2 - 16*n + 23).

23, 86, 284, 856, 2416, 6496, 16832, 42368, 104192, 251392, 596992, 1398784, 3239936, 7430144, 16891904, 38109184, 85393408, 190185472, 421265408, 928514048, 2037383168, 4452253696, 9693036544, 21030240256, 45483032576, 98079604736, 210923159552

Offset

4,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 4..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 (6,-12,8).

Formula

From Colin Barker, Oct 17 2012: (Start)

a(n) = 6*a(n-1) - 12*a(n-2) + 8*a(n-3).

G.f.: -x^4*(44*x^2 - 52*x + 23)/(2*x-1)^3. (End)

Mathematica

Table[2^(n-4) (4 n^2 - 16 n + 23), {n, 4, 30}] (* Vincenzo Librandi, Mar 11 2013 *)
LinearRecurrence[{6, -12, 8}, {23, 86, 284}, 30] (* Harvey P. Dale, Oct 06 2019 *)

Prog

(Maxima) makelist(2^(n-4)*(4*n^2-16*n+23), n, 4, 30); /* Martin Ettl, Oct 15 2012 */
(Magma) [2^(n-4)*(4*n^2-16*n+23): n in [4..30]]; // Vincenzo Librandi, Mar 11 2013

Crossrefs

Sequence in context: A056580 A010011 A172117 * A284711 A193018 A044210

Adjacent sequences: A217526 A217527 A217528 * A217530 A217531 A217532

Keyword

nonn,easy

Author

N. J. A. Sloane, Oct 13 2012

Status

approved