OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) <= n.
From Robert Israel, Aug 10 2016: (Start)
a(n) >= sqrt(n).
If n is prime or the square of a prime, then a(n) = n.
If n = m^j, then a(n) <= m^ceiling((j+1)/2). (End)
EXAMPLE
a(54) = 9 because 54 divides phi(9^2) = 54.
MAPLE
N:= 100: # to get a(1)..a(N)
S:= {$1..N}: A:= 'A':
for k from 1 while S <> {} do
r:= numtheory:-phi(k^2);
E:= select(t -> r mod t = 0, S);
if E <> {} then
assign(seq(A[e], e=E) = seq(k , e=E));
S:= S minus E;
fi
od:
seq(A[i], i=1..N); # Robert Israel, Aug 10 2016
MATHEMATICA
Table[k = 1; While[! Divisible[EulerPhi[k^2], n], k++]; k, {n, 80}] (* Michael De Vlieger, Aug 10 2016 *)
PROG
(PARI) a(n) = {my(k=1); while(eulerphi(k^2) % n, k++); k; }
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Altug Alkan, Aug 10 2016
STATUS
approved