The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A008330 phi(p-1), as p runs through the primes. 43
 1, 1, 2, 2, 4, 4, 8, 6, 10, 12, 8, 12, 16, 12, 22, 24, 28, 16, 20, 24, 24, 24, 40, 40, 32, 40, 32, 52, 36, 48, 36, 48, 64, 44, 72, 40, 48, 54, 82, 84, 88, 48, 72, 64, 84, 60, 48, 72, 112, 72, 112, 96, 64, 100, 128, 130, 132, 72, 88, 96, 92, 144, 96, 120, 96, 156, 80, 96, 172, 112 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Number of primitive roots in the field with p elements. Kátai proves that phi(p-1)/(p-1) has a continuous distribution function. - Charles R Greathouse IV, Jul 15 2013 For odd primes p, phi(p-1)<=(p-1)/2 since p has phi(p-1) primitive roots and (p-1)/2 quadratic residues and no primitive root is a quadratic residue. - Geoffrey Critzer, Apr 18 2015 LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 P. Erdős, On the density of some sequences of numbers, III., J. London Math. Soc. 13 (1938), pp. 119-127. Imre Kátai, On distribution of arithmetical functions on the set prime plus one, Compositio Math. 19 (1968), pp. 278-289. I. J. Schoenberg, Über die asymptotische Verteilung reeller Zahlen mod 1, Mathematische Zeitschrift 28:1 (1928), pp. 171-199. FORMULA a(n) = phi(phi(prime(n))). - Robert G. Wilson v, Dec 26 2015 a(n) = phi(A006093(n)). - Michel Marcus, Dec 27 2015 MAPLE A008330 := proc(n)     numtheory[phi](ithprime(n)-1) ; end proc: seq(A008330(n), n=1..100) ; MATHEMATICA Table[ EulerPhi[ Prime@n - 1], {n, 70}] (* Robert G. Wilson v, Dec 17 2005 *) PROG (PARI) a(n)=eulerphi(prime(n)-1) \\ Charles R Greathouse IV, Dec 08 2011 (MAGMA) [EulerPhi(NthPrime(n)-1): n in [1..80]]; // Vincenzo Librandi, Apr 06 2015 CROSSREFS Cf. A000010, A241194, A241195 (fraction phi(p-1)/(p-1)), A338364 (partial products). Sequence in context: A175359 A336125 A330807 * A191234 A225373 A138219 Adjacent sequences:  A008327 A008328 A008329 * A008331 A008332 A008333 KEYWORD nonn,look AUTHOR STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 23 08:11 EST 2021. Contains 340385 sequences. (Running on oeis4.)