OFFSET
0,2
COMMENTS
Also sequence found by reading the segment (1, 18) together with the line from 18, in the direction 18, 74,..., in the square spiral whose vertices are the generalized dodecagonal numbers A195162. - Omar E. Pol, Nov 02 2012
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
M. Baake and U. Grimm, Coordination sequences for root lattices and related graphs, arXiv:cond-mat/9706122, Zeit. f. Kristallographie, 212 (1997), 253-256.
R. Bacher, P. de la Harpe and B. Venkov, Séries de croissance et séries d'Ehrhart associées aux réseaux de racines, C. R. Acad. Sci. Paris, 325 (Series 1) (1997), 1137-1142.
Index entries for linear recurrences with constant coefficients, signature (3, -3, 1).
FORMULA
a(n) = 20*n^2-4*n+2, for n>0.
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3) for n>3. G.f.: (1+15*x+23*x^2+x^3)/(1-x)^3. [Colin Barker, Apr 13 2012]
MATHEMATICA
CoefficientList[Series[(1+15*x+23*x^2+x^3)/(1-x)^3, {x, 0, 40}], x] (* Vincenzo Librandi, Apr 20 2012 *)
Join[{1}, LinearRecurrence[{3, -3, 1}, {18, 74, 170}, 40]] (* Harvey P. Dale, Dec 03 2012 *)
PROG
(Magma) [1] cat [20*n^2-4*n+2: n in [1..40]]; // Vincenzo Librandi, Apr 20 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
mbaake(AT)sunelc3.tphys.physik.uni-tuebingen.de (Michael Baake)
STATUS
approved