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 A112728 #11 Jul 21 2025 16:18:58
%S A112728 1,37044,1222452,193637687880
%N A112728 Numbers k such that geometric mean of phi(k), k and sigma(k) is an integer.
%C A112728 It is interesting that a(2) divides a(3).
%C A112728 There is no further term up to 6*10^8.
%C A112728 a(5) > 4*10^11. - _Giovanni Resta_, Jul 13 2013
%e A112728 (phi(1222452)*1222452*sigma(1222452))^(1/3)=1164240 is an integer, so 1222452 is a term of the sequence.
%t A112728 Do[If[IntegerQ[(n*DivisorSigma[1, n] EulerPhi[n])^(1/3)], Print[n]], {n, 600000000}]
%Y A112728 Cf. A011257.
%K A112728 more,nonn
%O A112728 1,2
%A A112728 _Farideh Firoozbakht_, Dec 01 2005
%E A112728 a(4) from _Giovanni Resta_, Jul 13 2013