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A231896 a(n) = 4*a(n-1) - a(n-2) with a(0) = 0, a(1) = 4. 3
0, 4, 16, 60, 224, 836, 3120, 11644, 43456, 162180, 605264, 2258876, 8430240, 31462084, 117418096, 438210300, 1635423104, 6103482116, 22778505360, 85010539324, 317263651936, 1184044068420, 4418912621744, 16491606418556, 61547513052480, 229698445791364 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
Number of domino tilings of a 2 X (2n-1) projective plane.
Numbers m such that 3*m^2+16 is a square. [Bruno Berselli, Dec 16 2014]
LINKS
W. K. Alt, Enumeration of Domino Tilings on the Projective Grid Graph, A Thesis Presented to The Division of Mathematics and Natural Sciences, Reed College, May 2013.
Hacène Belbachir, Soumeya Merwa Tebtoub, and László Németh, Ellipse Chains and Associated Sequences, J. Int. Seq., Vol. 23 (2020), Article 20.8.5.
FORMULA
G.f.: 4*x/(1-4*x+x^2). - Philippe Deléham, Nov 19 2013
a(n) = ((2*(-(2-sqrt(3))^n+(2+sqrt(3))^n)))/sqrt(3). - Colin Barker, Oct 12 2015
MATHEMATICA
LinearRecurrence[{4, -1}, {0, 4}, 30] (* Harvey P. Dale, Oct 01 2015 *)
PROG
(PARI) concat(0, Vec(4*x/(1-4*x+x^2) + O(x^40))) \\ Colin Barker, Oct 12 2015
CROSSREFS
Equals 4*A001353.
Sequence in context: A267928 A269532 A269673 * A128650 A072335 A081161
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 18 2013
EXTENSIONS
More terms and other edits by M. F. Hasler, Nov 20 2013
STATUS
approved

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Last modified April 16 03:28 EDT 2024. Contains 371696 sequences. (Running on oeis4.)