A068422 Numbers n such that n-phi(n) divides sigma(n).

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

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

Cf. A000010, A000203, A055164.

Sequence in context: A325396 A326533 A144147 * A085118 A276579 A166158

Adjacent sequences: A068419 A068420 A068421 * A068423 A068424 A068425

Keyword

easy,nonn

Author

Benoit Cloitre, Mar 02 2002

Status

approved