A326817 Numbers k such that phi(k) > phi(k+1) > phi(k+2) > phi(k+3) where phi is the Euler totient function (A000010).

823, 943, 3133, 4387, 4873, 5443, 5563, 5863, 7213, 7753, 7873, 8383, 9007, 10333, 10693, 11113, 11503, 12043, 12763, 13483, 13843, 13921, 14623, 14683, 16573, 16663, 16963, 16993, 17113, 17983, 19003, 19093, 19303, 20083, 20143, 20953, 21613, 21733, 22513

Offset

1,1

References

Jean-Marie De Koninck, Those Fascinating Numbers, American Mathematical Society, 2009, page 106, entry 823.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

823 is in the sequence since phi(823) = 822, phi(824) = 408, phi(825) = 400, phi(826) = 348, and 822 > 408 > 400 > 348.

Mathematica

aQ[n_] := AllTrue[Differences @ EulerPhi[n + Range[0, 3]], # < 0 &]; Select[Range[23000], aQ] (* Amiram Eldar, Oct 20 2019 *)

Crossrefs

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

Subsequence of A328056.

Sequence in context: A103764 A189121 A364538 * A271044 A252539 A033531

Adjacent sequences: A326814 A326815 A326816 * A326818 A326819 A326820

Keyword

nonn

Author

Kritsada Moomuang, Oct 20 2019

Status

approved