cp's OEIS Frontend

A238226 Numbers k such that if x = sigma(k) + tau(k) - k then k = sigma(x) + tau(x) - x.

%I A238226 #24 Jul 12 2019 17:54:21
%S A238226 1,3,14,52,130,144,184,274,300,586,656,8648,10434,11470,12008,15774,
%T A238226 17034,18802,19270,21032,22088,22184,23288,34688,35394,36872,38744,
%U A238226 39790,65324,65392,67628,68476,153868,163676,188468,198628,254526,263890,379026,463390
%N A238226 Numbers k such that if x = sigma(k) + tau(k) - k then k = sigma(x) + tau(x) - x.
%C A238226 A083874 is a subset of this sequence: it lists the fixed points of the transform n -> sigma(n)+tau(n)-n.
%H A238226 Amiram Eldar, <a href="/A238226/b238226.txt">Table of n, a(n) for n = 1..900</a> (terms 1..50 from Paolo P. Lava)
%e A238226 Fixed points: 1, 3, 14, 52, 130, 184, 656, 8648, 12008, 34688, ...
%e A238226 sigma(144) = 403, tau(144) = 15 and 403 + 15 - 144 = 274.
%e A238226 sigma(274) = 414, tau(274) = 4 and 414 + 4 - 274 = 144.
%p A238226 with(numtheory); P:=proc(q)local a,n;
%p A238226 for n from 1 to q do a:=sigma(n)+tau(n)-n;
%p A238226 if sigma(a)+tau(a)-a=n then print(n);
%p A238226 fi; od; end: P(10^6);
%t A238226 f[n_] := DivisorSigma[0, n] + DivisorSigma[1, n] - n; s={}; Do[m = f[n]; If[f[m] == n, AppendTo[s, n]], {n, 1, 500000}]; s (* _Amiram Eldar_, Jul 12 2019 *)
%Y A238226 Cf. A000005, A000203, A083874, A238225, A238227-A238230.
%K A238226 nonn
%O A238226 1,2
%A A238226 _Paolo P. Lava_, Feb 20 2014