This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A008421 #26 Jul 08 2025 01:03:52
%S A008421 1,21,221,1561,8361,36365,134245,433905,1256465,3317445,8097453,
%T A008421 18474633,39753273,81270333,158819253,298199265,540279585,948062325,
%U A008421 1616336765,2684641785,4354393801,6911195501,10753517061,16429137361,24680949041,36503969061
%N A008421 Crystal ball sequence for 10-dimensional cubic lattice.
%C A008421 This is row/column 10 of the Delannoy numbers array, A008288, which is the main entry for these numbers, listing many more properties. - _Peter Munn_, Jan 05 2023
%H A008421 T. D. Noe, <a href="/A008421/b008421.txt">Table of n, a(n) for n = 0..1000</a>
%H A008421 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 A008421 <a href="/index/Cor#crystal_ball">Index entries for crystal ball sequences</a>
%H A008421 <a href="/index/Rec#order_11">Index entries for linear recurrences with constant coefficients</a>, signature (11, -55, 165, -330, 462, -462, 330, -165, 55, -11, 1).
%F A008421 G.f.: (1+x)^10/(1-x)^11.
%F A008421 a(n) = (4*n^10+20*n^9+330*n^8+1200*n^7+7392*n^6+18060*n^5+50270*n^4 +71800*n^3+83754*n^2+50670*n+14175)/14175 - _Johannes W. Meijer_, Jul 14 2013
%t A008421 CoefficientList[Series[-(z + 1)^10/(z - 1)^11, {z, 0, 200}], z] (* _Vladimir Joseph Stephan Orlovsky_, Jun 19 2011 *)
%Y A008421 Cf. A001847, A001848, A001849, A008288, A240876.
%K A008421 nonn,easy
%O A008421 0,2
%A A008421 _N. J. A. Sloane_