A015849 Numbers n such that phi(n + 9) | sigma(n) for n not congruent to 0 (mod 3).

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

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