Function: istotient
Section: number_theoretical
C-Name: istotient
Prototype: lGD&
Help: istotient(x,{&N}): true(1) if x = eulerphi(n) for some integer n,
 false(0) if not. If N is given, set N = n as well.
Doc: true (1) if $x = \phi(n)$ for some integer $n$, false (0)
 if not.
 \bprog
 ? istotient(14)
 %1 = 0
 ? istotient(100)
 %2 = 0
 @eprog
 If $N$ is given, set $N = n$ as well.
 \bprog
 ? istotient(4, &n)
 %1 = 1
 ? n
 %2 = 10
 @eprog
