|
|
A067780
|
|
Numbers n such that sigma(n)/phi(n) is prime.
|
|
1
|
|
|
2, 3, 12, 15, 35, 56, 78, 140, 190, 357, 630, 812, 910, 1045, 1672, 2214, 2580, 3339, 4180, 4522, 4674, 5049, 5278, 5544, 8008, 10659, 11160, 12441, 16065, 16120, 16770, 18630, 18810, 24244, 24871, 24969, 25070, 25758, 27000, 27170, 28896
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
sigma(12)/phi(12) = 28/4 = 7, a prime, so 12 is a term of the sequence.
|
|
MATHEMATICA
|
Select[Range[10^5], PrimeQ[DivisorSigma[1, # ]/EulerPhi[ # ]] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|