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 A005048 #32 Jun 18 2018 03:26:49
%S A005048 4,5,7,8,9,12,14,16,18,20,22,24,26,27,29,32,33,36,39,42,44,47,49,52,
%T A005048 53,57,59,63,65,67,69,73,76,78,81,83,86,90,92,96,98,100,103,104,106,
%U A005048 111,113,119,121,125,128,131,133,137,140
%N A005048 Minimal span of set of n elements with no 4-term arithmetic progression.
%C A005048 If the first appearance of n in A003003 is A003003(k) = n, then a(n) = k-1. - _Robert Israel_, Mar 21 2016
%H A005048 B. E. Brown and D. M. Gordon, <a href="http://dx.doi.org/10.1090/S0025-5718-96-00765-X">On sequences without geometric progressions</a>, Math. Comp. 65 (1996), no. 216, 1749-1754.
%H A005048 Sean A. Irvine, <a href="/A005048/a005048.out.txt">Example sets for a(4)-a(27)</a>
%e A005048 Example for n=13: { 1, 2, 3, 5, 6, 8, 9, 10, 16, 17, 18, 20, 21 } with span 20.
%Y A005048 Cf. A005047, A005049, A005050.
%K A005048 nonn,more
%O A005048 4,1
%A A005048 _N. J. A. Sloane_
%E A005048 Corrected and extended by _David W. Wilson_, May 15 1997
%E A005048 a(22)-a(26) from _Sean A. Irvine_, Mar 17 2016
%E A005048 a(24)-a(26) corrected by _Robert Israel_, Mar 20 2016
%E A005048 a(27) from _Sean A. Irvine_, Mar 20 2016
%E A005048 a(28)-a(34) from _Robert Israel_, Mar 21 2016
%E A005048 a(35)-a(58) from _Fausto A. C. Cariboni_, Jun 17 2018