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 A087887 #13 Feb 22 2025 17:49:16
%S A087887 0,24,168,540,1248,2400,4104,6468,9600,13608,18600,24684,31968,40560,
%T A087887 50568,62100,75264,90168,106920,125628,146400,169344,194568,222180,
%U A087887 252288,285000,320424,358668,399840,444048,491400,542004,595968,653400,714408,779100,847584
%N A087887 a(n) = 18n^3 + 6n^2.
%C A087887 Another parametric representation of the solutions of the Diophantine equation x^2 - y^2 = z^3 is (x,y,z) = (15n^3, 3n^3, 6n^2), thus getting a(n) = 18n^3 + 6n^2.
%F A087887 O.g.f.: 12x(2+6x+x^2)/(-1+x)^4. a(n) = 12*A036659(n). - _R. J. Mathar_, Apr 07 2008
%F A087887 From _Amiram Eldar_, Jan 10 2023: (Start)
%F A087887 Sum_{n>=1} 1/a(n) = Pi^2/36 + sqrt(3)*Pi/12 + 3*log(3)/4 - 3/2.
%F A087887 Sum_{n>=1} (-1)^(n+1)/a(n) = Pi^2/72 - sqrt(3)*Pi/6 - log(2) + 3/2. (End)
%t A087887 a[n_] := 18*n^3 + 6*n^2; Array[a, 50, 0] (* _Amiram Eldar_, Jan 10 2023 *)
%Y A087887 Cf. A036659, A085409, A085482.
%K A087887 easy,nonn
%O A087887 0,2
%A A087887 Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Oct 13 2003
%E A087887 More terms from _Ray Chandler_, Nov 06 2003