A067229 Numbers n such that phi(2n+1) = sigma(n).
6, 7, 27, 38, 55, 85, 87, 127, 188, 236, 255, 266, 445, 451, 655, 717, 913, 1309, 1357, 1490, 1947, 2095, 2515, 2726, 3002, 3247, 3289, 4117, 4237, 5071, 5605, 7195, 8924, 12128, 12625, 12771, 12837, 13190, 13795, 15835, 16197, 16748, 17997, 20257
Offset: 1
Keywords
Links
- Donovan Johnson, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Select[Range[21000],EulerPhi[2#+1]==DivisorSigma[1,#]&] (* Harvey P. Dale, Sep 06 2024 *)
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PARI
isok(n) = eulerphi(2*n+1) == sigma(n); \\ Michel Marcus, Nov 21 2013