A066231 Numbers n such that phi(n) = phi(n-1) - phi(n-2).
6, 8, 26, 78, 218, 306, 3666, 4646, 5066, 8816, 12206, 12546, 19878, 20436, 24236, 29546, 37736, 47996, 60116, 72086, 73026, 77046, 87476, 121146, 126056, 129246, 149756, 190268, 234636, 247856, 273296, 275724, 419366, 531236, 553476, 621726
Offset: 1
Keywords
Examples
phi(8) = 4 = 6-2 = phi(7) - phi(6).
Links
- Harry J. Smith and Jud McCranie, Table of n, a(n) for n = 1..494 (first 117 terms from Harry J. Smith)
Programs
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Mathematica
Flatten[Position[Partition[EulerPhi[Range[630000]],3,1],?(#[[3]] == #[[2]]- #[[1]]&),1,Heads->False]]+2 (* _Harvey P. Dale, Aug 19 2018 *)
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PARI
n=0; for (m=3, 10^9, if (eulerphi(m) == eulerphi(m - 1) - eulerphi(m - 2), write("b066231.txt", n++, " ", m); if (n==117, return)) ) \\ Harry J. Smith, Feb 06 2010
Extensions
a(24)-a(36) from Harry J. Smith, Feb 06 2010
Comments