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 A335253 #12 May 30 2020 04:08:52 %S A335253 12,76,488,556,1100,1430,2408,8896,538208,13685780,962402768 %N A335253 Numbers k such that the abundance (A033880) of k is equal to the deficiency (A033879) of k+2. %C A335253 Equivalently, k and k+2 have the same absolute value of abundance (or deficiency) with opposite signs. %C A335253 Equivalently, s(k) + s(k+2) = k + (k+2), where s(k) is the sum of proper divisors of k (A001065). %C A335253 a(12) > 10^11, if it exists. %C A335253 a(12) > 10^13, if it exists. - _Giovanni Resta_, May 30 2020 %e A335253 12 is a term since A033880(12) = sigma(12) - 2*12 = 28 - 24 = 4, and A033879(14) = 2*14 - sigma(14) = 28 - 24 = 4. %t A335253 ab[n_] := DivisorSigma[1, n] - 2*n; Select[Range[10^5], ab[#] == -ab[# + 2] &] %o A335253 (PARI) isok(k) = sigma(k) + sigma(k+2) == 4*k+4; \\ _Michel Marcus_, May 29 2020 %Y A335253 Cf. A000203, A001065, A033879, A033880, A330901, A335254. %K A335253 nonn,more %O A335253 1,1 %A A335253 _Amiram Eldar_, May 28 2020