OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
EXAMPLE
18 = phi(19) = phi(27) = phi(38) = phi(54).
MATHEMATICA
a = Table[ 0, {2500} ]; Do[ p = EulerPhi[ n ]; If[ p < 2501, a[ [ p ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 2500 ], a[ [ # ] ] == 4 & ]
PROG
(PARI) is(k) = invphiNum(k) == 4 \\ Amiram Eldar, Nov 17 2024, using Max Alekseyev's invphi.gp
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Apr 18 2001
STATUS
approved