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 A033885 #28 Jul 02 2025 16:01:56
%S A033885 2,3,5,5,9,6,13,9,14,12,21,8,25,18,21,17,33,15,37,18,31,30,45,12,44,
%T A033885 36,41,28,57,18,61,33,51,48,57,17,73,54,61,30,81,30,85,48,57,66,93,20,
%U A033885 90,57,81,58,105,42,93,48,91,84,117,12,121,90,85,65,111,54,133,78,111,66
%N A033885 a(n) = 3*n - sum of divisors of n.
%C A033885 The first zero term occurs at n = 120. The first negative term is a(180) = -6. For any k, k*n - sigma(n) is negative for some n. See A023199. - _T. D. Noe_, Aug 07 2003
%H A033885 Ivan Neretin, <a href="/A033885/b033885.txt">Table of n, a(n) for n = 1..10000</a>
%F A033885 a(n) = A008585(n) - A000203(n). - _Omar E. Pol_, Sep 30 2017
%F A033885 Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = 3 - zeta(2) = 1.355065... . - _Amiram Eldar_, Mar 25 2024
%e A033885 For n=4, 3n=12, sum of divisors of n is 1+2+4=7, so a(4)=12-7=5.
%p A033885 with(numtheory): for n from 1 to 150 do printf(`%d,`,3*n-sigma(n)) od:
%t A033885 Table[3 n - DivisorSigma[1, n], {n, 70}] (* _Ivan Neretin_, Sep 30 2017 *)
%o A033885 (PARI) a(n)=3*n-sigma(n) \\ _Charles R Greathouse IV_, Mar 16 2016
%Y A033885 Cf. A000203, A008585, A013661, A023199.
%K A033885 sign,easy
%O A033885 1,1
%A A033885 _N. J. A. Sloane_
%E A033885 More terms from _James Sellers_, Jun 01 2000