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

1,1

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)

Example

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

Mathematica

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

Prog

(PARI) for (n=2, 3000, if (eulerphi(n-1)<eulerphi(n) && eulerphi(n)<eulerphi(n+1), print1(n", ")))

Crossrefs

Cf. A000010.

Sequence in context: A070796 A045093 A304978 * A188006 A160725 A044338

Adjacent sequences: A078773 A078774 A078775 * A078777 A078778 A078779

Keyword

nonn

Author

Jon Perry, Jan 09 2003

Extensions

More terms from Michel Marcus, Mar 17 2014

Status

approved