OFFSET
1,3
COMMENTS
The sequence differs from A065394 since it is not monotonic.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
a(1) = sigma(phi(2))- phi(sigma(2)) = sigma(1)-phi(3) = 1-2 = -1.
MATHEMATICA
Table[DivisorSigma[1, p-1] - EulerPhi[p+1], {p, Prime[Range[100]]}] (* Amiram Eldar, Jun 09 2024 *)
PROG
(Magma) [DivisorSigma(1, EulerPhi(p))-EulerPhi(DivisorSigma(1, p)): p in PrimesUpTo(400)]; // Bruno Berselli, Oct 20 2015
CROSSREFS
KEYWORD
sign,look
AUTHOR
Labos Elemer, Mar 03 2004
STATUS
approved