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 A001219 #22 Feb 16 2025 08:32:22 %S A001219 0,6,120,210,990,185136,258474216 %N A001219 Triangular numbers of form a(a+1)(a+2). %D A001219 R. K. Guy, Unsolved Problems in Number Theory, D3. %H A001219 S. P. Mohanty, <a href="http://dx.doi.org/10.1007/BF01903544">Which triangular numbers are products of three consecutive integers?</a>, Acta Mathematica Hungarica 1991, Volume 58, Issue 1-2, pp 31-36. %H A001219 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularNumber.html">Triangular Number.</a> %F A001219 a(n) = A000217(A097571(n)). - _Michel Marcus_, Jan 14 2015 %p A001219 count:= 0: %p A001219 for a from 0 to 637 do %p A001219 p:= a*(a+1)*(a+2); %p A001219 if issqr(1+8*p) then %p A001219 count:= count+1; %p A001219 A[count]:= p; %p A001219 fi %p A001219 od: %p A001219 seq(A[i],i=1..count); # _Robert Israel_, Jan 14 2015 %t A001219 Select[Times @@@ Partition[Range[0, 700], 3, 1], OddQ[ Sqrt[ 8 # + 1]] &] (* _Harvey P. Dale_, Nov 04 2017 *) %Y A001219 Cf. A000217, A097571. %K A001219 nonn,fini,full %O A001219 1,2 %A A001219 _N. J. A. Sloane_