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Numbers k such that both k and 2*k are balanced numbers (A020492).
4

%I #16 Dec 04 2019 09:59:30

%S 1,3,6,15,35,70,105,210,357,420,1045,1485,2090,2970,3135,3339,5049,

%T 5940,6270,10659,12441,12540,16065,24871,24969,29029,33915,35343,

%U 39105,39585,49742,50065,58058,58435,64285,70686,71145,74613,78210,87087

%N Numbers k such that both k and 2*k are balanced numbers (A020492).

%H Amiram Eldar, <a href="/A076375/b076375.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson)

%t f[x_] := DivisorSigma[1, x]/EulerPhi[x] Do[s=f[n]; s1=f[2*n]; If[IntegerQ[s]&&IntegerQ[s1], Print[n]], {n, 1, 100000}]

%Y Cf. A000010, A000203, A055234.

%K nonn

%O 1,2

%A _Labos Elemer_, Oct 15 2002