A078776 Numbers k such that phi(k-1) < phi(k) < phi(k+1), where phi is the Euler totient function (A000010).

106, 166, 316, 526, 586, 736, 1156, 1366, 1485, 1486, 1576, 1756, 1786, 1816, 1996, 2146, 2206, 2416, 2476, 2535, 2536, 2806, 2836, 3003, 3004, 3046, 3316, 3466, 3675, 3676, 3886, 3927, 3928, 4096, 4126, 4306, 4455, 4456, 4485, 4486, 4516, 4726, 4785, 4786

Offset: 1

Author

Jon Perry, Jan 09 2003

Keywords

• nonn

Examples

			phi(105)=48 < phi(106)=52 < phi(107)=106, so 106 is in the sequence.
		

References

• Jean-Marie De Koninck, Those Fascinating Numbers, American Mathematical Society, 2009, page 34, entry 105.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)

Crossrefs

Cf. A000010.

Programs

Mathematica

Flatten[Position[Partition[EulerPhi[Range[5000]],3,1],?(Min[Differences[ #]]> 0&)]//Quiet]+1 (* _Harvey P. Dale, Jun 14 2019 *)

PARI

for (n=2,3000, if (eulerphi(n-1)
				

Extensions

More terms from Michel Marcus, Mar 17 2014