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 A335389 #5 Jun 05 2020 09:58:33
%S A335389 49,324,1024,1444,1681,2600,9800,265225,332928,379456,421200,1940449,
%T A335389 4198400,4293184,4739328,8346320,11309768,27050400,65918161,203694425,
%U A335389 384199200,418488849,546717924,2239277041,2687489280,4866742025,5783450400,6933892900,7725003664
%N A335389 Numbers k such that k and k+1 are both antiharmonic numbers (A020487).
%C A335389 Terms of this sequence k such that k and k+1 are both nonsquares (A227771) are 203694425, 4866742025, ...
%C A335389 Can two consecutive numbers be both primitive antiharmonic numbers (A228023)? Numbers k such that k and k+2 are both primitive antiharmonic numbers exist - the first two are 38246258 and 344321280.
%e A335389 49 is a term since both 49 and 50 are antiharmonic: sigma_2(49)/sigma(49) = 43 and sigma_2(50)/sigma(50) = 35 are both integers.
%t A335389 antihQ[n_] := Divisible[DivisorSigma[2, n], DivisorSigma[1, n]]; seq = {}; q1 = antihQ[1]; Do[q2 = antihQ[n]; If[q1 && q2, AppendTo[seq, n - 1]]; q1 = q2, {n, 2, 2 * 10^6}]; seq
%Y A335389 Cf. A000203, A001157, A020487, A227771, A228023.
%K A335389 nonn
%O A335389 1,1
%A A335389 _Amiram Eldar_, Jun 04 2020