OFFSET
1,2
COMMENTS
Even numbers that are not the terms of this sequence are 12, 102, 114, 130, ...
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
FORMULA
MATHEMATICA
psi[n_] := If[n < 1, 0, n Sum[ MoebiusMu[d]^2/d, {d, Divisors@ n}]]; Array[psi@# - EulerPhi@# &, 87] (* Robert G. Wilson v, Sep 23 2017 *)
PROG
(PARI) a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));
a(n) = a001615(n) - eulerphi(n); \\ after Charles R Greathouse IV at A001615
CROSSREFS
KEYWORD
AUTHOR
Altug Alkan, Sep 23 2017
STATUS
approved