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 A350869 #27 Jan 27 2022 20:49:35
%S A350869 0,2025,24502500,249500250000,2499500025000000,24999500002500000000,
%T A350869 249999500000250000000000,2499999500000025000000000000,
%U A350869 24999999500000002500000000000000,249999999500000000250000000000000000,2499999999500000000025000000000000000000
%N A350869 a(n) = Sum_{i=0..10^n-1} i^3.
%C A350869 These terms k = x.y satisfy equation x.y = (x+y)^2, when x and y have the same number of digits, "." means concatenation, and y may not begin with 0. So, this is a subsequence of A350870 and A238237.
%H A350869 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (11100,-11100000,1000000000).
%F A350869 a(n) = 10^(2n) * (10^n-1)^2 / 4 = A037182(n)^2.
%F A350869 a(n) = A000217(10^n-1)^2.
%F A350869 a(n) = A038544(n) - 10^(3*n).
%e A350869 a(1) = Sum_{i=0..9} i^3 = (Sum_{i=0..9} i)^2 = 2025.
%t A350869 a[n_] := (10^n*(10^n - 1)/2)^2; Array[a, 11, 0] (* _Amiram Eldar_, Jan 20 2022 *)
%o A350869 (PARI) a(n) = my(x=10^n-1); (x*(x+1)/2)^2; \\ _Michel Marcus_, Jan 22 2022
%Y A350869 Cf. A000217, A037156, A037182, A038544, A238237.
%K A350869 nonn,base,easy
%O A350869 0,2
%A A350869 _Bernard Schott_, Jan 20 2022