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 A211487 Characteristic sequence of numbers n having a primitive root modulo n. 3
 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1 COMMENTS a(1) = 0, since we have an empty set of numbers more than 0 and less than 1. If A(x) is the counting function of a(n)=1, n<=x, then A(x)~2*x/log(x) as x tends to infinity. Characteristic function of A033948 (apart from the initial term). - Antti Karttunen, Aug 22 2017 LINKS Antti Karttunen, Table of n, a(n) for n = 1..65537 FORMULA a(n) = 1 iff n = 2, 4, p^k, 2*p^k, where p is an odd prime. A001783(n) ≡ (-1)^a(n) mod n. From Antti Karttunen, Aug 22 2017: (Start) For n > 1, if A034380(n) = 1, a(n) = 1, otherwise a(n) = 0. A103131(n) = (-1)^a(n) for n > 2. (End) PROG (PARI) A211487(n) = if(n%2, !!isprimepower(n), (n==2 || n==4 || (isprimepower(n/2, &n) && n>2))); \\ Antti Karttunen, Aug 22 2017, after Charles R Greathouse IV's code for A033948. CROSSREFS Cf. A001783, A033948, A034380, A103131. Sequence in context: A196147 A242647 A275606 * A252372 A204447 A188642 Adjacent sequences:  A211484 A211485 A211486 * A211488 A211489 A211490 KEYWORD nonn AUTHOR Vladimir Shevelev, May 13 2012 EXTENSIONS More terms from Antti Karttunen, Aug 22 2017 STATUS approved

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