OFFSET
1,1
COMMENTS
If p is an odd prime, p and 2*p are in the sequence but there are some other kinds of numbers as 99 or 168.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
filter:= proc(n) uses numtheory; type(sigma(n)/(n - phi(n)), integer) end proc:
select(filter, [$2..1000]); # Robert Israel, May 03 2019
MATHEMATICA
Select[Range[2, 200], Divisible[DivisorSigma[1, #], #-EulerPhi[#]]&] (* Harvey P. Dale, Mar 14 2011 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 02 2002
STATUS
approved