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 A118260 #11 Feb 16 2025 08:33:01 %S A118260 1,3,7,11,19,23,35,43,51,59,79,87,111,123,139,153,185,197,233,247,271, %T A118260 291,335,351,377,401,427,445,501,517,577,603,643,675,723,745,817,853, %U A118260 901,929,1009,1033,1117,1151,1187,1231,1323,1353,1405,1439,1503,1541 %N A118260 Number of weakly carefree couples (a,b) with a,b<=n. %C A118260 (a, b) is a weakly carefree couple if gcd(a, b) = 1 and either a or b is squarefree (A005117). - _Amiram Eldar_, Mar 03 2021 %D A118260 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 2.5.1 Carefree Couples, p. 110. %H A118260 Pieter Moree, <a href="https://arxiv.org/abs/math/0510003">Counting carefree couples</a>, arXiv:math/0510003 [math.NT], 2005-2014. %H A118260 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CarefreeCouple.html">Carefree Couple</a>. %F A118260 From _Amiram Eldar_, Mar 03 2021: (Start) %F A118260 a(n) = 2*A118258(n) - A118259(n). %F A118260 a(n) ~ A118261 * n^2 + O(n*log(n)). (End) %Y A118260 Cf. A005117, A118258, A118259, A118261. %K A118260 nonn %O A118260 1,2 %A A118260 _Eric W. Weisstein_, Apr 20 2006