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A048867 Numbers for which reduced residue system contains fewer primes than nonprimes. 3
1, 2, 11, 13, 17, 19, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 94, 95, 97, 99, 101, 103, 106, 107, 109, 111, 113, 115, 117, 118, 119, 121, 122, 123, 124, 125, 127, 128 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Integers n such that 2*A000720(n) - 2*A001221(n) < A000010(n).

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

EXAMPLE

Large primes belong to this set. Composites like: n=35 has 2 prime divisors, Phi(35)=24 Pi(35)=11; In reduced residue system 9 primes and 15 nonprimes occur.

MATHEMATICA

Select[Range[500], 2*PrimePi[#] - 2*PrimeNu[#] < EulerPhi[#] &] (* G. C. Greubel, May 12 2017 *)

PROG

(PARI) isok(n) = 2*(primepi(n) - omega(n)) < eulerphi(n); \\ Michel Marcus, May 13 2017

CROSSREFS

Cf. A000010, A000720, A001221.

Sequence in context: A286153 A068972 A116437 * A113626 A154539 A137238

Adjacent sequences:  A048864 A048865 A048866 * A048868 A048869 A048870

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified August 15 13:27 EDT 2020. Contains 336504 sequences. (Running on oeis4.)