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 A225745 #22 Sep 16 2020 14:12:10
%S A225745 1,2,3,5,6,8,9,10,13,15,17,19,21,23,25,27,28,30,33,34,37,40,43,45,48,
%T A225745 50,53,54,58,60,64,66,68,70,74,77,79,82,84,87,91
%N A225745 Smallest k such that n numbers can be picked in {1,...,k} with no four in arithmetic progression.
%D A225745 Knuth, Donald E., Satisfiability, Fascicle 6, volume 4 of The Art of Computer Programming. Addison-Wesley, 2015, pages 135 and 190, Problem 31.
%H A225745 Samuel S. Wagstaff, Jr., <a href="http://dx.doi.org/10.1090/S0025-5718-1972-0325500-5">On k-free sequences of integers</a>, Math. Comp., 26 (1972), 767-771.
%e A225745 a(8)=10 because of the unique solution 1 2 3 5 6 8 9 10.
%Y A225745 This sequence is to A003003 as A065825 is to A003002.
%K A225745 nonn,more
%O A225745 1,2
%A A225745 _Don Knuth_, Aug 05 2013
%E A225745 a(37)-a(41) from _Bert Dobbelaere_, Sep 16 2020