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 A076786 #8 Aug 23 2020 11:39:23
%S A076786 1,2,3,5,6,7,10,11,13,14,15,17,19,21,22,23,26,29,30,31,33,34,35,37,38,
%T A076786 39,51,53,55,57,58,59,61,62,65,66,67,69,70,71,73,74,77,78,79,101,102,
%U A076786 103,105,106,107,109,110,111,113,114,115,118,119,130,131,133,134,137
%N A076786 Squarefree numbers such that in decimal representation all their prefixes are also squarefree.
%C A076786 m is a term iff A008966(floor(m/10^k))=1 for 0<=k<=A004216(n);
%C A076786 a(n)=A005117(n) for n<=26, but A005117(27)=41 is not a term, as 4=2^2 is not squarefree.
%H A076786 Harvey P. Dale, <a href="/A076786/b076786.txt">Table of n, a(n) for n = 1..1000</a>
%e A076786 143=11*13 is a term, as also 14=2*7 and 1 are squarefree.
%t A076786 Select[Range[200],AllTrue[FromDigits/@Table[Take[IntegerDigits[#],{1,n}],{n,IntegerLength[#]}],SquareFreeQ]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 23 2020 *)
%K A076786 nonn,base
%O A076786 1,2
%A A076786 _Reinhard Zumkeller_, Nov 16 2002