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 A343725 #22 May 28 2021 02:20:35
%S A343725 4,64,484,8464,88804,868624,8880400,86862400,888040000,8880800644,
%T A343725 88864802404,888868068804,8886826042084,88886806880400,
%U A343725 888686062262244,8888680688040000,88868606226224400,888868068804000000,8888600480200862404,88886806880400000000
%N A343725 a(n) is the largest n-digit square with all digits even.
%H A343725 Chai Wah Wu, <a href="/A343725/b343725.txt">Table of n, a(n) for n = 1..63</a>
%o A343725 (Python 3.8+)
%o A343725 from math import isqrt
%o A343725 def A343725(n):
%o A343725 m = isqrt(8*(10**i-1)//9)
%o A343725 m -= m % 2
%o A343725 k = m**2
%o A343725 s = set('02468')
%o A343725 while not set(str(k)) <= s:
%o A343725 m -= 2
%o A343725 k -= 4*(m+1)
%o A343725 return k # _Chai Wah Wu_, May 20 2021
%Y A343725 Cf. A030098, A343724.
%K A343725 nonn,base
%O A343725 1,1
%A A343725 _Jon E. Schoenfield_, May 19 2021