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 A049688 #36 Oct 06 2019 18:19:02
%S A049688 0,2,5,10,17,28,41,60,83,112,145,188,235,294,359,432,513,610,713,834,
%T A049688 963,1104,1255,1428,1609,1810,2023,2254,2497,2768,3047,3356,3681,4026,
%U A049688 4387,4772,5169,5602,6053,6528,7019
%N A049688 a(n) = Sum_{i=0..n} T(i,n-i), array T as in A049687.
%C A049688 A131967(a(n)+1) = 1, A131967(a(n)) = 2. - _Birkas Gyorgy_, Feb 19 2011
%C A049688 Number of triples {A, B, C} where 1 <= A <= B <= C <= n+1 and gcd(C-B, B-A) = 1. E.g., for n=2, we have the 5 triples {1, 1, 2}, {1, 2, 2}, {2, 2, 3}, {2, 3, 3}, and {1, 2, 3}. - _Griffin N. Macris_, May 21 2016
%H A049688 Griffin N. Macris, <a href="/A049688/b049688.txt">Table of n, a(n) for n = 0..99999</a>
%F A049688 a(n) ~ n^2*(3+n) / Pi^2. - _Griffin N. Macris_, May 21 2016
%t A049688 Table[Sum[Sum[EulerPhi[j], {j, i}] + 1, {i, n}], {n, 0, 30}] (* _Birkas Gyorgy_, Feb 19 2011 *)
%t A049688 Table[n + Sum[ EulerPhi[ j], {i, n}, {j, i}], {n, 0, 30}] (* _Robert G. Wilson v_, Feb 12 2015 *)
%Y A049688 Cf. A049687, A131967.
%K A049688 nonn
%O A049688 0,2
%A A049688 _Clark Kimberling_