OFFSET
1,1
COMMENTS
No more terms < 30000. All terms, except the first, are multiples of 3. - Emeric Deutsch, Jun 25 2005
a(11) > 5*10^10. - Donovan Johnson, Jun 10 2011
No other terms < 10^12. - Jud McCranie, Aug 27 2013
EXAMPLE
sf(363) = 220, phi(363) = 220.
MAPLE
with(numtheory): a:=proc(n) if add(mobius(k)^2, k=1..n-1)=phi(n) then n else fi end: seq(a(n), n=1..5000); # Emeric Deutsch, Jun 25 2005
PROG
(PARI) sf(n)=s=0; for(x=1, n, if(issquarefree(x), s++)); s; for(n=1, 10^5, if(sf(n)==eulerphi(n), print(n)))
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Jason Earls, Sep 07 2001
EXTENSIONS
Corrected and extended by Emeric Deutsch, Jun 25 2005
a(9) from Donovan Johnson, Jul 15 2009
a(10) from Donovan Johnson, Jun 10 2011
STATUS
approved