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A064020 Numbers n such that sf(n) = phi(n), where sf(n) = A013928(n). 0
2, 3, 9, 33, 363, 1089, 1653, 3237, 4297761, 32348343651 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..10.

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

Sequence in context: A277345 A259943 A296263 * A204442 A306523 A095412

Adjacent sequences:  A064017 A064018 A064019 * A064021 A064022 A064023

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

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Last modified June 2 08:00 EDT 2020. Contains 334767 sequences. (Running on oeis4.)