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 A119522 #6 Feb 24 2019 04:36:03
%S A119522 1,-8,-27,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%T A119522 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%U A119522 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
%N A119522 Determinant of n X n matrix of first n^2 nonzero terms of triangular numbers.
%F A119522 a(n) = determinant of n X n matrix of first n^2 nonzero terms of A000217(k) for k>0. a(n) = determinant of n X n matrix of k*(k+1)/2 for k from 1 through n^2.
%e A119522 a(3) = -27 =
%e A119522 |.1..3..6|
%e A119522 |10.15.21|
%e A119522 |28.36.45|.
%e A119522 a(4) = 0 because of the singular matrix 0 =
%e A119522 |.1...3...6..10|
%e A119522 |15..21..28..36|
%e A119522 |45..55..66..78|
%e A119522 |91.105.120.136|.
%t A119522 nmax = 100; Table[Det[Table[(k*(i-1) + j)*(k*(i-1) + j + 1)/2, {i, 1, k}, {j, 1, k}]], {k, 1, nmax}] (* _Vaclav Kotesovec_, Feb 24 2019 *)
%Y A119522 Cf. A000217, A119493.
%K A119522 easy,sign
%O A119522 1,2
%A A119522 _Jonathan Vos Post_, May 27 2006
%E A119522 More terms from _Vaclav Kotesovec_, Feb 24 2019