A327880 Numbers k such that phi(k) < phi(k+1) < phi(k+2) < phi(k+3) where phi is the Euler totient function (A000010).

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

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