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A068422
Numbers n such that n-phi(n) divides sigma(n).
3
2, 3, 5, 6, 7, 10, 11, 13, 14, 17, 19, 22, 23, 26, 29, 31, 34, 37, 38, 41, 43, 46, 47, 53, 58, 59, 61, 62, 67, 71, 73, 74, 79, 82, 83, 86, 89, 94, 97, 99, 101, 103, 106, 107, 109, 113, 118, 122, 127, 131, 134, 137, 139, 142, 146, 149, 151, 157, 158, 163, 166, 167, 168
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
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