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A328056 Numbers k such that phi(k) > phi(k+1) > phi(k+2) where phi is the Euler totient function (A000010). 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 21 03:58 EST 2022. Contains 350473 sequences. (Running on oeis4.)