A064020 Numbers n such that sf(n) = phi(n), where sf(n) = A013928(n).

2, 3, 9, 33, 363, 1089, 1653, 3237, 4297761, 32348343651

Offset: 1

Author

Jason Earls, Sep 07 2001

Keywords

• more
• nonn

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

Examples

			sf(363) = 220, phi(363) = 220.
		

Programs

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

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)))

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