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 A104882 #7 Sep 08 2022 08:45:17
%S A104882 1,1,2,3,5,8,14,24,45,85,170,351,749,1656,3758,8776,21013,51473,
%T A104882 129018,329939,860901,2288528,6192526,17047248,47693661,135554549,
%U A104882 391099370,1144867871,3398656893,10226072720,31173964942,96240485104,300777706053
%N A104882 Diagonal sums of number triangle A104881.
%H A104882 G. C. Greubel, <a href="/A104882/b104882.txt">Table of n, a(n) for n = 0..1000</a>
%F A104882 a(n) = Sum_{k=0..floor(n/2)} ( Sum_{j=0..k} (n-2*k)^(k-j) ).
%F A104882 a(n) = Sum_{k=0..floor(n/2)} A104881(n-k, k).
%t A104882 Table[Sum[If[j==k, 1, (n-2*k)^(k-j)], {k, 0, Floor[n/2]}, {j,0,k}], {n,0,40}] (* _G. C. Greubel_, Jun 15 2021 *)
%o A104882 (Magma) [(&+[ (&+[ (n-2*k)^(k-j) : j in [0..k]]) : k in [0..Floor(n/2)]]): n in [0..40]]; // _G. C. Greubel_, Jun 15 2021
%o A104882 (Sage) [sum(sum((n-2*k)^(k-j) for j in (0..k)) for k in (0..n//2)) for n in (0..40)] # _G. C. Greubel_, Jun 15 2021
%Y A104882 Cf. A104879, A104881.
%K A104882 easy,nonn
%O A104882 0,3
%A A104882 _Paul Barry_, Mar 28 2005