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 A140288 #17 Aug 27 2019 10:26:25
%S A140288 5,25,125,3125,53125,453125,4453125,14453125,314453125,2314453125,
%T A140288 22314453125,122314453125,4122314453125,44122314453125,
%U A140288 444122314453125,4444122314453125,54444122314453125,254444122314453125,1254444122314453125,21254444122314453125
%N A140288 The least n-digit multiple of 5^n using the decimal digits {1, 2, 3, 4, 5} exclusively.
%H A140288 Alois P. Heinz, <a href="/A140288/b140288.txt">Table of n, a(n) for n = 1..1000</a>
%F A140288 To obtain the (n+1)-th term, write the n-th term as k * 5^n. Multiply k by a multiple of 2^n to get a multiple of 5. Add the multiplicator of 2^n to the left of the n-th term.
%e A140288 a(5) = 53125 = 17 * 5^5.
%o A140288 (PARI) lista(nn) = {v = vector(nn); v[1] = 5; for(k = 2, nn, j = 1; while((j*10^(k-1) + v[k-1]) % 5^k > 0, j++); v[k] = j*10^(k-1) + v[k-1]); for(k = 1, nn, print1(v[k], ", "));} \\ _Jinyuan Wang_, Aug 27 2019
%Y A140288 Cf. A053312, A035014.
%K A140288 nonn,base
%O A140288 1,1
%A A140288 Michel Criton (mcriton(AT)wanadoo.fr), May 24 2008
%E A140288 More terms from _Alois P. Heinz_, Apr 05 2017