OFFSET
1,1
COMMENTS
The fixed points (terms with x = n) are 2, 4, 20, 66, 342, 41922, 10983114, ... - Amiram Eldar, Mar 31 2019
LINKS
Kevin P. Thompson, Table of n, a(n) for n = 1..38
EXAMPLE
Fixed points: 2, 4, 20, 66, 342, 41922, ...
Amicable pairs: (34092, 40842), (46242, 55422), (207624, 259448), ...
sigma(34092) = 86268, phi(34092) = 11352, tau(34092) = 18 and 86268 - 11352 + 18 - 34092 = 40842.
sigma(40842) = 88530, phi(40842) = 13608, tau(40842) = 12 and 88530 - 13608 + 12 - 40842 = 34092.
MAPLE
with(numtheory); P:=proc(q)local a, n;
for n from 1 to q do a:=sigma(n)-phi(n)+tau(n)-n;
if a>0 and sigma(a)-phi(a)+tau(a)-a=n then print(n);
fi; od; end: P(10^6);
MATHEMATICA
f[n_] := If[n > 0, DivisorSigma[1, n] - EulerPhi[n] + DivisorSigma[0, n] - n, 0]; s={}; Do[ If[f[f[n]] == n, AppendTo[s, n]], {n, 1, 60000}]; s (* Amiram Eldar, Mar 31 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Feb 20 2014
EXTENSIONS
a(11)-a(29) from Amiram Eldar, Mar 31 2019
a(30) from Giovanni Resta, Apr 04 2019
STATUS
approved