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
Keywords
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Crossrefs
Cf. A015827.
Programs
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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
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Mathematica
Select[Range[1, 5000], Divisible[DivisorSigma[1, #], EulerPhi[9 + #]] && ! Mod[#, 3] == 0 &] (* David Nacin, Mar 04 2012 *)
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PARI
is(n)=n%3 && sigma(n)%eulerphi(n+9)==0 \\ Charles R Greathouse IV, Sep 25 2012
Comments