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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 Table of n, a(n) for n=1..21. 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 Cf. A000005, A000010, A000203, A077092. Sequence in context: A275253 A034725 A047929 * A264202 A338783 A324304 Adjacent sequences: A243992 A243993 A243994 * A243996 A243997 A243998 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.)