OFFSET
1,4
COMMENTS
a(p) = 1 for p prime. Otherwise a(n) is even.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
EXAMPLE
a(10) = 6 because sigma(10) = 18 and phi(10) = 4, and so phi(18 - 4) = phi(14) = 6.
a(11) = 1 because sigma(11) = 12 and phi(11) = 10, so phi(12 - 10) = phi(2) = 1.
a(12) = 8 because sigma(12) = 28 and phi(12) = 4, so phi(28 - 4) = phi(24) = 8.
MAPLE
with(numtheory); A077088:=n->phi(sigma(n)-phi(n)); seq(A077088(n), n=1..100); # Wesley Ivan Hurt, Dec 02 2013
MATHEMATICA
Table[EulerPhi[DivisorSigma[1, n] - EulerPhi[n]], {n, 100}] (* Alonso del Arte, Nov 29 2013 *)
PROG
(PARI) A077088(n) = if(1==n, 0, eulerphi(sigma(n) - eulerphi(n))); \\ Antti Karttunen, Mar 04 2018
(GAP) List([1..100], n->Phi(Sigma(n)-Phi(n))); # Muniru A Asiru, Mar 04 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Labos Elemer, Nov 04 2002
EXTENSIONS
Value of a(1) clarified by Antti Karttunen, Mar 04 2018
STATUS
approved