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%I #22 May 30 2026 16:40:03
%S 1,882,130242,7796978,255582978,5369283570,79749022402,895903147122,
%T 7996359740418,58861356563058,367891005738690,1998142759241202,
%U 9609441659124482,41553956372047602,163646115158499522,593216067051658610,1997319977281662978,6294200366345505138,18687294283503843522
%N Coordination sequence for C_21 lattice.
%H Seiichi Manyama, <a href="/A035758/b035758.txt">Table of n, a(n) for n = 0..10000</a>
%H R. Bacher, P. de la Harpe and B. Venkov, <a href="https://doi.org/10.1016/S0764-4442(97)83542-2">Séries de croissance et séries d'Ehrhart associées aux réseaux de racines</a>, C. R. Acad. Sci. Paris, 325 (Series 1) (1997), 1137-1142.
%H J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices VII: Coordination Sequences, Proc. Royal Soc. London, A453 (1997), 2369-2389 (<a href="http://neilsloane.com/doc/Me220.pdf">pdf</a>).
%H Joan Serra-Sagrista, <a href="https://doi.org/10.1016/S0020-0190(00)00119-8">Enumeration of lattice points in l_1 norm</a>, Inf. Proc. Lett. 76 (1-2) (2000) 39-44.
%F a(n) = [x^(2n)] ((1+x)/(1-x))^21.
%K nonn,easy,changed
%O 0,2
%A Joan Serra-Sagrista (jserra(AT)ccd.uab.es)
%E Recomputed by _N. J. A. Sloane_, Nov 25 1998