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 A066294 #17 Mar 22 2020 12:18:23 %S A066294 -2,0,0,20,0,82,0,124,60,174,0,550,0,298,286,588,0,1030,0,1178,482, %T A066294 642,0,2702,260,862,726,2030,0,3824,0,2540,1018,1398,934,6298,0,1714, %U A066294 1358,5810,0,6632,0,4406,3628,2442,0,11870,700,5294,2182,5930,0,10192,1902,10038,2666,3774,0,22644,0,4282,6140,10540,2506 %N A066294 a(n) = A000203(n)^2 - A001157(n) - 2n = sigma(n)^2 - sigma_2(n) - 2n. %C A066294 For primes p, a(p) = 0, otherwise positive, except for n = 1 where it is negative. %H A066294 Amiram Eldar, <a href="/A066294/b066294.txt">Table of n, a(n) for n = 1..10000</a> %t A066294 a[n_] := DivisorSigma[1,n]^2 - DivisorSigma[2,n] - 2n; Array[a, 65] (* _Amiram Eldar_, Jul 31 2019 *) %o A066294 (PARI) a(n) = sigma(n)^2 - sigma(n, 2) - 2*n; \\ _Michel Marcus_, Mar 22 2020 %Y A066294 Cf. A000203, A001157. %K A066294 sign %O A066294 1,1 %A A066294 _Labos Elemer_, Dec 12 2001