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 A219428 a(n) = n - 1 - phi(n). 2
 -1, 0, 0, 1, 0, 3, 0, 3, 2, 5, 0, 7, 0, 7, 6, 7, 0, 11, 0, 11, 8, 11, 0, 15, 4, 13, 8, 15, 0, 21, 0, 15, 12, 17, 10, 23, 0, 19, 14, 23, 0, 29, 0, 23, 20, 23, 0, 31, 6, 29, 18, 27, 0, 35, 14, 31, 20, 29, 0, 43, 0, 31, 26, 31, 16, 45, 0, 35, 24, 45, 0, 47 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS Apart from the first term, the same as A016035. For n > 1, a(n) is also the number of numbers below n which are not coprime to n. a(n) = 0 if n is prime. x^(n - 1 - phi(n)) is congruent to x^(n - 1) mod n, if x is coprime to n, since x^phi(n) is congruent to 1 (mod n) if x is coprime to n. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = n - 1 - A000010(n) = A051953(n) - 1 = cototient(n) - 1. - Omar E. Pol, Nov 21 2012 MATHEMATICA Table[n - (EulerPhi[n] + 1), {n, 75}] (* Alonso del Arte, Nov 17 2012 *) PROG (PARI) for(n=1, 100, print1(n-1-eulerphi(n)", ")) (MAGMA) [(n - 1 - (EulerPhi(n))): n in [1..100]]; // Vincenzo Librandi, Jan 26 2013 CROSSREFS Cf. A000010, A219029. Sequence in context: A274715 A324180 A271860 * A016035 A297168 A112470 Adjacent sequences:  A219425 A219426 A219427 * A219429 A219430 A219431 KEYWORD sign,easy AUTHOR V. Raman, Nov 20 2012 STATUS approved

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Last modified September 30 12:21 EDT 2020. Contains 337439 sequences. (Running on oeis4.)