|
|
A067612
|
|
Numbers n such that sigma(n) = 3*phi(sigma(n)).
|
|
1
|
|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Numbers n such that sigma(n) is in A033845.
|
|
LINKS
|
|
|
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:
|
|
MATHEMATICA
|
s3pQ[n_]:=Module[{s=DivisorSigma[1, n]}, s==3*EulerPhi[s]]; Select[ Range[ 400], s3pQ] (* Harvey P. Dale, May 28 2015 *)
|
|
PROG
|
(PARI) for(n=1, 500, if(sigma(n)==3*eulerphi(sigma(n)), print1(n, ", "))) \\ Derek Orr, Feb 26 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|