A091454 Integers k such that 3*phi(k) < k.

30, 42, 60, 66, 78, 84, 90, 102, 114, 120, 126, 132, 138, 150, 156, 168, 174, 180, 186, 198, 204, 210, 222, 228, 234, 240, 246, 252, 258, 264, 270, 276, 282, 294, 300, 306, 312, 318, 330, 336, 342, 348, 354, 360, 366, 372, 378, 390, 396, 402, 408, 414, 420

Offset: 1

Author

Robert G. Wilson v, Jan 10 2004

Keywords

• nonn

Comments

If k is present so are all m*k, m>1.

The smallest odd number in this sequence is 111546435 = 3*5*7*11*...*23. - T. D. Noe, Jan 15 2004

Links

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

Crossrefs

Cf. A000010 (phi), A054741, A066765, A091456.

Programs

Magma

[k:k in [1..500]|3*EulerPhi(k) lt k]; // Marius A. Burtea, Jan 13 2020

Maple

filter:= n -> 3*numtheory:-phi(n) < n:
select(filter, [$1..10000]); # Robert Israel, Jan 13 2020

Mathematica

Select[ Range[437], 3EulerPhi[ # ] < # & ]

PARI

is(n) = 3*eulerphi(n) < n; \\ Amiram Eldar, Apr 07 2024