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 A256631 #19 Jan 19 2020 13:07:13
%S A256631 50,105,150,205,350,450,500,501,502,505,550,1005,1015,1050,1055,1105,
%T A256631 1150,1205,1450,1500,1501,1550,2005,2050,2055,2105,2305,2350,3350,
%U A256631 3500,4500,5000,5001,5002,5005,5010,5011,5012,5015,5020,5021,5032,5045,5050,5055
%N A256631 Numbers n such that the decimal expansions of both n and n^2 have 0 as smallest digit and 5 as largest digit.
%H A256631 Felix Fröhlich, <a href="/A256631/b256631.txt">Table of n, a(n) for n = 1..10000</a>
%t A256631 fQ[n_] := Block[{c = DigitCount@ n}, And[Plus @@ Take[c, {6, 9}] == 0, c[[5]] > 0, c[[10]] > 0]]; Select[Range@ 5100, fQ@ # && fQ[#^2] &] (* _Michael De Vlieger_, Apr 12 2015 *)
%t A256631 Select[Range[5100],Min[IntegerDigits[#]]==0&&Max[IntegerDigits[#] ]== 5 && Min[IntegerDigits[#^2]]==0&&Max[IntegerDigits[#^2]]==5&] (* _Harvey P. Dale_, Jan 19 2020 *)
%o A256631 (PARI) is(n) = vecmin(digits(n))==0 && vecmin(digits(n^2))==0 && vecmax(digits(n))==5 && vecmax(digits(n^2))==5
%Y A256631 Cf. A136817, A256630, A256633, A256634, A256708, A256709, A256889, A257086.
%K A256631 nonn,base
%O A256631 1,1
%A A256631 _Felix Fröhlich_, Apr 05 2015