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A243995 Fixed points of the function a(n) = phi(sigma(n) - phi(n) - d(n)), where phi(n) is the Euler totient function, sigma(n) the sum of divisors of n and d(n) the number of divisors of n. 1
1, 18, 96, 560, 720, 1056, 1760, 2000, 3264, 7392, 30960, 50800, 172080, 173440, 9561600, 13304064, 195522560, 1017856448, 1026021024, 1568010240, 2817884160 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
a(22) > 10^10. - Amiram Eldar, Jan 27 2019
LINKS
EXAMPLE
sigma(96) = 252, phi(96) = 32, d(96) = 12 and phi(252 - 32 - 12) = 96.
MAPLE
with(numtheory): P:=proc(q) local n;
for n from 1 to q do
if phi(sigma(n)-phi(n)-tau(n))=n then print(n);
fi; od; end: P(10^10);
MATHEMATICA
Select[Range[10^4], EulerPhi[DivisorSigma[1, #] - EulerPhi[#] - DivisorSigma[0, #]] == # &] (* Alonso del Arte, Jun 18 2014 *)
PROG
(PARI) isok(n) = (spd = sigma(n) - eulerphi(n) - numdiv(n)) && (eulerphi(spd) == n); \\ Michel Marcus, Jun 18 2014
CROSSREFS
Sequence in context: A275253 A034725 A047929 * A264202 A338783 A324304
KEYWORD
nonn,more
AUTHOR
Paolo P. Lava, Jun 18 2014
EXTENSIONS
a(15)-a(16) from Jens Kruse Andersen, Jul 23 2014
a(17)-a(21) from Amiram Eldar, Jan 27 2019
STATUS
approved

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Last modified June 19 17:53 EDT 2024. Contains 373507 sequences. (Running on oeis4.)