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 A187264 #10 Mar 30 2012 17:37:34
%S A187264 1,3,7,11,21,25,43,54,73,83,125,136,194,215,245,278,374,396,516,552,
%T A187264 614,662,834,871,1018,1087,1215,1285,1555,1592,1900,2023,2181,2298,
%U A187264 2506,2581,3013,3160,3378,3497,4027,4105,4689,4875,5103
%N A187264 Number of nonempty subsets of {1, 2, ..., n} with <=3 pairwise coprime elements.
%H A187264 Alois P. Heinz, <a href="/A187264/b187264.txt">Table of n, a(n) for n = 1..10000</a>
%F A187264 a(n) = A187262(n,3).
%e A187264 a(4) = 11 because there are 11 nonempty subsets of {1,2,3,4} with <=3 pairwise coprime elements: {1}, {2}, {3}, {4}, {1,2}, {1,3}, {1,4}, {2,3}, {3,4}, {1,2,3}, {1,3,4}.
%Y A187264 Column 3 of triangle A187262. First differences are A186987.
%K A187264 nonn
%O A187264 1,2
%A A187264 _Alois P. Heinz_, Mar 07 2011