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 A077681 #13 Nov 05 2017 01:43:50
%S A077681 5,51,53,55,57,58,59,501,502,503,505,506,509,510,511,514,515,517,518,
%T A077681 519,521,523,526,527,530,533,534,535,537,538,541,542,543,545,546,547,
%U A077681 551,553,554,555,557,559,561,562,563,565,566,569,570,571,573,574,577
%N A077681 Squarefree numbers beginning with 5.
%C A077681 Lower density is 3/(25*Pi^2), upper density is 10/(9*Pi^2). - _Charles R Greathouse IV_, Nov 05 2017
%H A077681 Harvey P. Dale, <a href="/A077681/b077681.txt">Table of n, a(n) for n = 1..5000</a>
%t A077681 Table[Select[Range[5*10^n,6*10^n-1],SquareFreeQ],{n,0,2}]//Flatten (* _Harvey P. Dale_, Apr 15 2017 *)
%o A077681 (PARI) is(n)=n>4 && digits(n)[1]==5 && issquarefree(n) \\ _Charles R Greathouse IV_, Nov 05 2017
%Y A077681 Cf. A077677, A077678, A077679, A077680, A077682, A077683, A077684, A077685.
%K A077681 base,easy,nonn
%O A077681 1,1
%A A077681 _Amarnath Murthy_, Nov 16 2002
%E A077681 More terms from _Sascha Kurz_, Jan 28 2003