A328056 Numbers k such that phi(k) > phi(k+1) > phi(k+2) where phi is the Euler totient function (A000010).

313, 523, 733, 823, 824, 943, 944, 973, 1153, 1363, 1573, 1753, 1783, 1813, 1993, 2143, 2413, 2473, 2623, 2803, 3043, 3133, 3134, 3253, 3313, 3463, 3703, 3883, 4093, 4123, 4303, 4387, 4388, 4513, 4723, 4873, 4874, 4933, 5113, 5143, 5353, 5443, 5444, 5563, 5564

Offset

1,1

Comments

Contains all members k of A206581 such that k==103 (mod 210) except 103.- Robert Israel, Oct 16 2019

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

313 is in the sequence since phi(313) = 312, phi(314) = 156, phi(315) = 144, and 312 > 156 > 144.

Maple

R:= NULL: count:= 0:
q:= false: s:= 0:
for i from 1 while count < 100 do
  t:= numtheory:-phi(i);
  r:= q;
  q:= evalb(t<s);
  if r and q then count:= count+1; R:= R, i-2 fi;
  s:= t;
od:
R; # Robert Israel, Oct 16 2019

Mathematica

Flatten[Position[Partition[EulerPhi[Range[5600]], 3, 1], _?(Max[Differences[#]] < 0 &)] // Quiet] (* Amiram Eldar, Oct 06 2019 after Harvey P. Dale at A078776 *)

Prog

(Magma) [k:k in [1..5600]| EulerPhi(k) gt EulerPhi(k+1) and EulerPhi(k+1) gt EulerPhi(k+2)]; // Marius A. Burtea, Oct 07 2019

Crossrefs

Cf. A000010, A078776, A161962, A161963, A206581, A327880.

Supersequence of A326817.

Sequence in context: A093808 A257527 A142745 * A142951 A176571 A142628

Adjacent sequences: A328053 A328054 A328055 * A328057 A328058 A328059

Keyword

nonn

Author

Kritsada Moomuang, Oct 03 2019

Status

approved