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 A356592 #21 Sep 14 2022 08:26:16
%S A356592 0,0,0,0,7,0,0,13,13,0,0,20,24,20,0,0,24,37,37,24,0,0,31,44,57,44,31,
%T A356592 0,0,37,57,68,68,57,37,0,0,44,68,88,81,88,68,44,0,0,51,81,105,105,105,
%U A356592 105,81,51,0,0,57,94,125,125,136,125,125,94,57,0
%N A356592 Array A(n, k), n, k >= 0, read by antidiagonals; A(n, k) = Sum_{i, j >= 3} t_i * u_j * T(i+j) where Sum_{i >= 3} t_i * T(i) and Sum_{j >= 3} u_j * T(j) are the greedy tribonacci representations of n and k, respectively, and T = A000073.
%C A356592 This sequence is to tribonacci numbers (A000073) what A135090 is to Fibonacci numbers (A000045).
%H A356592 A. Messaoudi, <a href="http://dx.doi.org/10.1016/S0893-9659(02)00073-3">Tribonacci multiplication</a>, Appl. Math. Lett. 15 (2002), 981-985.
%H A356592 Rémy Sigrist, <a href="/A356592/a356592.gp.txt">PARI program</a>
%H A356592 <a href="/index/Z#Zeckendorf">Index entries for sequences related to Zeckendorf expansion of n</a>
%F A356592 A(n, 0) = A(0, k) = 0.
%F A356592 A(n, k) = A(k, n).
%F A356592 A(m, A(n, k)) = A(A(m, n), k) for m, n, k >= 5.
%e A356592 Array A(n, k) begins:
%e A356592 n\k | 0 1 2 3 4 5 6 7 8 9 10
%e A356592 ----+---------------------------------------------------
%e A356592 0 | 0 0 0 0 0 0 0 0 0 0 0
%e A356592 1 | 0 7 13 20 24 31 37 44 51 57 64
%e A356592 2 | 0 13 24 37 44 57 68 81 94 105 118
%e A356592 3 | 0 20 37 57 68 88 105 125 145 162 182
%e A356592 4 | 0 24 44 68 81 105 125 149 173 193 217
%e A356592 5 | 0 31 57 88 105 136 162 193 224 250 281
%e A356592 6 | 0 37 68 105 125 162 193 230 267 298 335
%e A356592 7 | 0 44 81 125 149 193 230 274 318 355 399
%e A356592 8 | 0 51 94 145 173 224 267 318 369 412 463
%e A356592 9 | 0 57 105 162 193 250 298 355 412 460 517
%e A356592 10 | 0 64 118 182 217 281 335 399 463 517 581
%o A356592 (PARI) See Links section.
%Y A356592 Cf. A000045, A000073, A101330, A135090.
%K A356592 nonn,tabl
%O A356592 0,5
%A A356592 _Rémy Sigrist_, Sep 11 2022