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 A156899 #11 Oct 30 2017 22:39:30
%S A156899 1,2,3,5,5,7,9,11,13,13,13,17,19,19,19,23,25,29,29,31,32,32,32,37,37,
%T A156899 37,41,41,43,43,47,49,53,53,53,53,59,61,61,64,64,67,67,67,71,73,73,73,
%U A156899 73,79,81,83,83,83,83,89,89,89,89,89,97,101,101,103,103,103,107,109,109
%N A156899 a(n) = the largest prime power <= the n-th positive squarefree integer.
%C A156899 The first positive squarefree integer is considered to be 1 here.
%H A156899 Michael De Vlieger, <a href="/A156899/b156899.txt">Table of n, a(n) for n = 1..10000</a>
%t A156899 Block[{nn = 110, s}, s = Select[Range[nn], SquareFreeQ]; Map[If[# == 1, 1, SelectFirst[# - Range[0, # - 1], PrimePowerQ]] &, s]] (* _Michael De Vlieger_, Oct 30 2017 *)
%Y A156899 Cf. A081217, A156898, A156900, A005117, A000961.
%K A156899 nonn
%O A156899 1,2
%A A156899 _Leroy Quet_, Feb 17 2009
%E A156899 Extended by _Ray Chandler_, Jun 19 2009