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 A209187 #29 Jul 20 2025 13:12:51
%S A209187 1,2,3,5,5,8,7,11,10,12,11,20,13,16,17,23,17,27,19,30,23,24,23,44,26,
%T A209187 28,31,40,29,50,31,47,35,36,37,67,37,40,41,66,41,66,43,60,57,48,47,92,
%U A209187 50,63,53,70,53,84,57,88,59,60,59,124,61,64,77,95,67,98,67,90,71,98,71
%N A209187 Sum of divisors of n minus cototient of n.
%H A209187 Ivan Neretin, <a href="/A209187/b209187.txt">Table of n, a(n) for n = 1..10000</a>
%H A209187 PrimeFan, <a href="http://primefan.tripod.com/EsotericIntegerSequences.html">Listing of Esoteric Integer Sequences</a>.
%H A209187 PrimeFan, <a href="/A031214/a031214.pdf">Esoteric Integer Sequences</a> [Cached copy]
%F A209187 a(n) = A065387(n) - n. - _Altug Alkan_, Sep 30 2017
%F A209187 a(n) = A000203(n) - A051953(n). - _Omar E. Pol_, Sep 30 2017
%F A209187 Sum_{k=1..n} a(k) = c * n^2 / 2 + O(n*log(n)), where c = 6/Pi^2 + Pi^2/6 - 1 = 1.252861... . - _Amiram Eldar_, Dec 08 2023
%t A209187 Table[(Plus @@ Divisors[n]) - (n - EulerPhi[n]), {n, 50}]
%o A209187 (PARI) a(n) = sigma(n) + eulerphi(n) - n; \\ _Altug Alkan_, Sep 30 2017
%o A209187 (SageMath) [sigma(n,1)+euler_phi(n)-n for n in range(1, 72)] # _Stefano Spezia_, Jul 20 2025
%Y A209187 Cf. A000203, A051953, A065387.
%Y A209187 Cf. A013661, A059956.
%K A209187 nonn,easy
%O A209187 1,2
%A A209187 _N. J. A. Sloane_, Mar 05 2012