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 A053317 #12 Oct 12 2022 13:34:58
%S A053317 2,52,552,5552,55552,255552,5255552,55255552,255255552,2255255552,
%T A053317 22255255552,222255255552,5222255255552,55222255255552,
%U A053317 255222255255552,2255222255255552,22255222255255552,222255222255255552
%N A053317 a(n) contains n digits (either '2' or '5') and is divisible by 2^n.
%H A053317 Robert Israel, <a href="/A053317/b053317.txt">Table of n, a(n) for n = 1..999</a>
%F A053317 a(n) = a(n-1) + 10^(n-1)*(2 + 3*(a(n-1)/2^(n-1) mod 2)), i.e., a(n) ends with a(n-1); if a(n-1) is divisible by 2^n then a(n) begins with a 2, if not then a(n) begins with a 5.
%p A053317 A[1]:= 2:
%p A053317 for n from 2 to 100 do
%p A053317 if A[n-1] mod 2^n = 0 then A[n]:= A[n-1]+2*10^(n-1)
%p A053317 else A[n]:= A[n-1]+5*10^(n-1)
%p A053317 fi
%p A053317 od:
%p A053317 seq(A[i],i=1..100); # _Robert Israel_, Oct 27 2019
%t A053317 Table[Select[FromDigits/@Tuples[{2,5},n],Divisible[#,2^n]&],{n,18}]//Flatten (* _Harvey P. Dale_, Oct 12 2022 *)
%Y A053317 Cf. A023398, A050621, A050622, A035014, A055880.
%K A053317 base,nonn
%O A053317 1,1
%A A053317 _Henry Bottomley_, Mar 06 2000
%E A053317 Formula corrected by _Robert Israel_, Oct 27 2019