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 A072961 #17 Mar 28 2023 07:59:17
%S A072961 2,5,22,25,52,55,222,225,252,255,522,525,552,555,2222,2225,2252,2255,
%T A072961 2522,2525,2552,2555,5222,5225,5252,5255,5522,5525,5552,5555,22222,
%U A072961 22225,22252,22255,22522,22525,22552,22555,25222,25225,25252,25255
%N A072961 Numbers using only the digits 2 and 5, that are both curved and straight.
%D A072961 M. J. Halm, Three Boxes, Puzzle-M Magazine (Apr. 1987).
%H A072961 Vincenzo Librandi, <a href="/A072961/b072961.txt">Table of n, a(n) for n = 1..8190</a>
%t A072961 Flatten[Table[FromDigits/@Tuples[{2, 5}, n], {n, 5}]] (* _Vincenzo Librandi_, Aug 19 2016 *)
%o A072961 (Python)
%o A072961 from itertools import product
%o A072961 A072961_list = [int(''.join(a)) for l in range(1,11) for a in product('25',repeat=l)] # _Chai Wah Wu_, May 12 2016
%o A072961 (Magma) [n: n in [1..30000] | Set(Intseq(n)) subset {2,5}]; // _Vincenzo Librandi_, Aug 19 2016
%K A072961 easy,nonn,base
%O A072961 1,1
%A A072961 _Michael Joseph Halm_, Aug 13 2002