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A015849 Numbers n such that phi(n + 9) | sigma(n) for n not congruent to 0 (mod 3). 2
5, 7, 10, 31, 47, 79, 127, 145, 161, 223, 238, 239, 355, 367, 371, 376, 418, 455, 463, 479, 748, 863, 1039, 1045, 1087, 1103, 1118, 1327, 1423, 1439, 1567, 1583, 1823, 1886, 1999, 2065, 2108, 2143, 2201, 2207, 2239, 2447, 2461, 2687, 2767, 2840, 2927, 2975 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Includes primes p such that (p+9)/8 is prime. Thus Dickson's conjecture implies the sequence is infinite. - Robert Israel, Jan 10 2019

LINKS

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

MAPLE

select(n -> (numtheory:-sigma(n)/numtheory:-phi(n+9))::integer, [seq(seq(3*i+j, j=1..2), i=0..1000)]); # Robert Israel, Jan 10 2019

MATHEMATICA

Select[Range[1, 5000], Divisible[DivisorSigma[1, #], EulerPhi[9 + #]] && ! Mod[#, 3] == 0 &] (* David Nacin, Mar 04 2012 *)

PROG

(PARI) is(n)=n%3 && sigma(n)%eulerphi(n+9)==0 \\ Charles R Greathouse IV, Sep 25 2012

CROSSREFS

Cf. A015827.

Sequence in context: A131998 A141443 A215660 * A059303 A061523 A119653

Adjacent sequences:  A015846 A015847 A015848 * A015850 A015851 A015852

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

STATUS

approved

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Last modified October 19 22:55 EDT 2019. Contains 328244 sequences. (Running on oeis4.)