OFFSET
1,2
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
FORMULA
a(n) > A063919(n) if n > 1.
a(A000040(k)) = 2.
Sum_{k=1..n} a(k) ~ c * n^2, where c = Pi^2/(12*zeta(3)) - 3/Pi^2 = 0.380252... . - Amiram Eldar, Aug 21 2023
EXAMPLE
a(1) = 1 - 1 = 0.
MATHEMATICA
Table[DivisorSum[n, # &, CoprimeQ[#, n/#] &] - EulerPhi@ n, {n, 120}] (* Michael De Vlieger, Mar 01 2017 *)
PROG
(PARI) a(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)) - eulerphi(n); \\ Michel Marcus, Feb 25 2014
(PARI) a(n)=my(f=factor(n)); prod(k=1, #f[, 2], f[k, 1]^f[k, 2]+1) - eulerphi(f) \\ Charles R Greathouse IV, Mar 01 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 03 2004
EXTENSIONS
Edited by R. J. Mathar, Mar 02 2009
STATUS
approved