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 A256889 #30 Mar 21 2022 08:01:57
%S A256889 115,1115,1235,3515,11115,12335,12415,33515,35415,123335,123512,
%T A256889 124235,145415,152132,231115,235211,333515,1114115,1155211,1233335,
%U A256889 1531115,1534312,2311115,3333515,11114115,11141115,11145511,12333335,12342335,15334312,15531115
%N A256889 Numbers k such that the decimal expansions of both k and k^2 have 1 as smallest digit and 5 as largest digit.
%C A256889 k can only begin with 1, 2 or 3 and k mod 10 can only equal 1, 2 or 5. - _Robert G. Wilson v_, Apr 13 2015
%C A256889 Heuristics suggest that this sequence should be infinite and the sequence with 4 in place of 5 should be finite. The latter sequence contains no terms up to 10^30. - _Charles R Greathouse IV_, Mar 20 2022
%H A256889 Chai Wah Wu, <a href="/A256889/b256889.txt">Table of n, a(n) for n = 1..2000</a> (n = 1..75 from Robert G. Wilson v).
%t A256889 fQ[n_] := Block[{c = DigitCount@ n}, And[Plus @@ Take[c, {6, 10}] == 0, c[[1]] > 0, c[[5]] > 0]]; Select[Range@ 100000, fQ@ # && fQ[#^2] &] (* _Michael De Vlieger_, Apr 12 2015 *)
%t A256889 fQ[n_] := Block[{id1 = Union@ IntegerDigits[ n], id2 = Union@ IntegerDigits[ n^2]}, Min[id1] == Min[id2] == 1 && Max[id1] == Max[id2] == 5]; k = 1; lst = {}; While[k < 10^7, If[ fQ@ k, AppendTo[lst, k]]; k++; If[ fQ@ k, AppendTo[lst, k]]; k += 3; If[ fQ@ k, AppendTo[lst, k]]; k += 6]; lst (* _Robert G. Wilson v_, Apr 13 2015 *)
%o A256889 (PARI) is(n) = vecmin(digits(n))==1 && vecmin(digits(n^2))==1 && vecmax(digits(n))==5 && vecmax(digits(n^2))==5
%Y A256889 Cf. A256630, A256631, A256633, A256634, A256708, A256709.
%K A256889 base,nonn
%O A256889 1,1
%A A256889 _Felix Fröhlich_, Apr 12 2015