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A327880 Numbers k such that phi(k) < phi(k+1) < phi(k+2) < phi(k+3) where phi is the Euler totient function (A000010). 3
1484, 2534, 3002, 3674, 3926, 4454, 4484, 4784, 4844, 5264, 5312, 5984, 6104, 7994, 8294, 8414, 8774, 8834, 9074, 9164, 9944, 10004, 10724, 11024, 11684, 11894, 12254, 13034, 13064, 13166, 13454, 13754, 14234, 15344, 15554, 16184, 16214, 16814, 17384, 17534 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Jean-Marie De Koninck, Those Fascinating Numbers, American Mathematical Society, 2009, p. 34, entry 105 and p. 130, entry 1484.

LINKS

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

EXAMPLE

1484 is in the sequence since phi(1484) = 624, phi(1485) = 720, phi(1486) = 742, and phi(1487) = 1486, and 624 < 720 < 742 < 1486.

MATHEMATICA

aQ[n_] := AllTrue[Differences @ EulerPhi[n + Range[0, 3]], # > 0 &]; Select[Range[18000], aQ]

PROG

(PARI) ok(k)={for(i=0, 2, if(eulerphi(k+i) >= eulerphi(k+i+1), return(0))); 1}

{ select(ok, [1..20000]) } \\ Andrew Howroyd, Sep 28 2019

CROSSREFS

Cf. A000010, A078776, A161962.

Sequence in context: A137365 A137366 A045008 * A257713 A269923 A288075

Adjacent sequences:  A327877 A327878 A327879 * A327881 A327882 A327883

KEYWORD

nonn

AUTHOR

Amiram Eldar, Sep 28 2019

STATUS

approved

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Last modified April 6 11:02 EDT 2020. Contains 333273 sequences. (Running on oeis4.)