A067612 Numbers n such that sigma(n) = 3*phi(sigma(n)).
5, 6, 10, 11, 14, 15, 17, 22, 23, 30, 33, 34, 35, 42, 46, 47, 51, 53, 55, 62, 66, 69, 70, 71, 77, 85, 94, 102, 105, 106, 107, 110, 115, 119, 138, 141, 142, 154, 155, 159, 161, 165, 170, 186, 187, 191, 210, 213, 214, 230, 231, 235, 238, 253, 254, 255, 265, 282, 310
Offset: 1
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
filter:= proc(n) local s; s:= numtheory:-sigma(n); s mod 6 = 0 and s = 2^padic:-ordp(s,2)*3^padic:-ordp(s,3) end proc: select(filter, [$1..10000]); # Robert Israel, Feb 26 2017
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Mathematica
s3pQ[n_]:=Module[{s=DivisorSigma[1,n]},s==3*EulerPhi[s]]; Select[ Range[ 400],s3pQ] (* Harvey P. Dale, May 28 2015 *) -
PARI
for(n=1,500,if(sigma(n)==3*eulerphi(sigma(n)),print1(n,", "))) \\ Derek Orr, Feb 26 2017
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PARI
is(n)=my(s=sigma(n)); s%3==0 && s==3*eulerphi(s) \\ Charles R Greathouse IV, Feb 27 2017
Comments