A333263 - OEIS

%I #4 Mar 13 2020 20:47:07

%S 5,447,700,3122,20649,25816,70221,205701,408624,2574176,3827656,

%T 4753563,12129928,118200807

%N Numbers k such that the sum of iterations of the alternating sum of divisors function A071324 starting from k is equal to 2*k.

%e 5 is a term since the iterations of A071324 with a starting value of 5 give A071324(5) = 4, A071324(4) = 3, A071324(3) = 2, and A071324(2) = 1, whose sum is 4 + 3 + 2 + 1 = 10 = 2 * 5.

%t f[n_] := Plus @@ (-(d = Divisors[n])*(-1)^(Range[Length[d],1,-1])); seqQ[n_]:=Plus @@ FixedPointList[f,n] == 3n + 1; Select[Range[10000], seqQ]

%Y Cf. A071324, A331017, A333262.

%K nonn,more

%O 1,1

%A _Amiram Eldar_, Mar 13 2020