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 A162500 #21 Sep 08 2022 08:45:46
%S A162500 1,3,6,9,12,15,17,18,18,17,15,12,9,6,3,1
%N A162500 Expansion of the polynomial (1-x^3) * (1-x^6) * (1-x^9) / (1-x)^3.
%C A162500 This is a row of the triangle A162499.
%C A162500 Only finitely many terms are nonzero.
%p A162500 m:=3: seq(coeff(series(mul((1-x^(3*i)),i=1..m)/(1-x)^m, x,n+1),x,n),n=0..16); # _Muniru A Asiru_, Jul 07 2018
%t A162500 CoefficientList[ Series[Times @@ (1 - x^(3 Range@3))/(1 - x)^3, {x, 0, 40}], x] (* _Wesley Ivan Hurt_, Sep 13 2014 and slightly modified by _Robert G. Wilson v_, Jul 23 2018 *)
%o A162500 (PARI) x='x+O('x^16); Vec((1-x^3)*(1-x^6)*(1-x^9)/(1-x)^3) \\ _G. C. Greubel_, Jul 06 2018
%o A162500 (Magma) m:=16; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1-x^3)*(1-x^6)*(1-x^9)/(1-x)^3)); /* complete row without zeros */ // _G. C. Greubel_, Jul 06 2018
%Y A162500 Cf. A162499.
%K A162500 nonn,fini,full
%O A162500 0,2
%A A162500 _N. J. A. Sloane_, Dec 02 2009