A376337 Numbers k such that phi(k)/2 + 1 = phi(k + 1) where phi = A000010.
3, 7, 9, 31, 127, 8191, 131071, 524287
Offset: 1
Examples
Number 9 is in this sequence because phi(9)/2 + 1 = 6/2 + 1 = 3 + 1 = 4 is equal to phi(9 + 1) = phi(10) = 4.
Programs
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Magma
[k: k in [3..5*10^6] | ((EulerPhi(k) div 2) + 1) eq EulerPhi(k + 1)];
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Mathematica
Select[Range[550000], EulerPhi[#]/2+1==EulerPhi[#+1] &] (* Stefano Spezia, Sep 22 2024 *)
Comments