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 A064670 #17 Aug 18 2024 16:42:54
%S A064670 1,1,4,5,20,36,61,244,504,576,1385,5540,11916,17280,14400,50521,
%T A064670 202084,442224,697536,792000,518400,2702765,10811060,23870196,
%U A064670 39202560,50198400,47174400,25401600,199360981,797443924,1769923944
%N A064670 Triangle T(n,k) (1 <= k <= n) where the first column (T(n,1)) is the sequence of secant numbers A000364.
%C A064670 Replacing m*m by m*(m+1) in the formula, the first column gives the tangent numbers A000182.
%F A064670 T(n+1, m) = m*m*Sum_{k = m-1..n} T(n, k) (T(n, 0) = 0).
%e A064670 T(4,3) = 9*(T(3,2) + T(3,3)) = 9*(20+36) = 504.
%t A064670 T[1, 1] = 1; T[n_, k_] /; 1 <= k <= n := T[n, k] = k^2*Sum[T[n-1, j], {j, k-1, n-1}]; T[_, _] = 0; Table[T[n, k], {n, 1, 8}, {k, 1, n}] // Flatten (* _Jean-François Alcover_, Oct 25 2016 *)
%Y A064670 Cf. A064190, A000182, A000354.
%K A064670 easy,nice,nonn,tabl
%O A064670 1,3
%A A064670 Jose L. Arregui (arregui(AT)posta.unizar.es), Oct 09 2001
%E A064670 More terms from _Philippe Deléham_, Sep 22 2005