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A119434 Odd n such that 2*phi(n) < n. 4
105, 165, 195, 315, 495, 525, 585, 735, 825, 945, 975, 1155, 1365, 1485, 1575, 1755, 1785, 1815, 1995, 2145, 2205, 2415, 2475, 2535, 2625, 2805, 2835, 2925, 3003, 3045, 3135, 3255, 3315, 3465, 3675, 3705, 3795, 3885, 3927, 4095, 4125, 4305, 4389, 4455 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Obviously 2*phi(n) = n is impossible for odd n. Odd elements of A054741 and A119432. This is not the same as A036798. 684411 = 3*7*13*23*109 is in this sequence but not in A036798. (This is may not be the smallest such value.) The primitive elements of this sequence are A119433, excluding the initial 2

If n is in the sequence, then so is every odd multiple of n. - Robert Israel, Jan 06 2017

LINKS

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

FORMULA

A036798 UNION A118700. - R. J. Mathar, Aug 08 2007

MAPLE

select(t -> numtheory:-phi(t) < t/2, [seq(t, t=1..10000, 2)]);

MATHEMATICA

Select[Range[1, 10^4, 2], 2 EulerPhi[#] < #&] (* Jean-Fran├žois Alcover, Apr 12 2019 *)

PROG

(PARI) lista(nn) = forstep (n=1, nn, 2, if (n > 2*eulerphi(n), print1(n, ", "))) \\ Michel Marcus, Jul 04 2015

CROSSREFS

Cf. A000010, A036798, A054741, A118700, A119432, A119433.

Sequence in context: A189936 A076762 A036798 * A091495 A256673 A046405

Adjacent sequences:  A119431 A119432 A119433 * A119435 A119436 A119437

KEYWORD

nonn

AUTHOR

Franklin T. Adams-Watters, May 19 2006

STATUS

approved

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Last modified May 24 17:16 EDT 2019. Contains 323533 sequences. (Running on oeis4.)