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 A070238 Sign of core(n)-phi(n) where core(n) is the squarefree part of n and phi the Euler totient function. 1
 0, 1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, 1, 1, 1, -1, -1, 1, -1, -1, 1, 1, 1, -1, 1, 1, 1, -1, 1, 1, 1, -1, 1, 1, 1, -1, -1, 1, 1, -1, -1, -1, 1, -1, 1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, 1, -1, -1, 1, 1, -1, 1, 1, 1, -1, 1, -1, 1, -1, 1, 1, 1, -1, 1, -1, -1, -1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Sum_{k=1..n} a(k) > 0 for n > 1. That is, the partial sums stay positive forever. For almost all n, a(n) = 2*mu(n)^2 - 1 = 2*A008966(n) - 1. Below 1000, there are only 5 exceptions: n=1, 420, 660, 780, 840. The exceptions are given by A070237. LINKS Antti Karttunen, Table of n, a(n) for n = 1..65537 FORMULA a(n) = sign(A007913(n) - A000010(n)). MATHEMATICA Array[Sign[Sqrt[#] /. (c_: 1) a_^(b_: 0) :> (c a^b)^2 - EulerPhi@ #] &, 100] (* Michael De Vlieger, Nov 18 2017, after Bill Gosper at A007913 *) PROG (PARI) for(n=1, 100, print1(sign(core(n)-eulerphi(n)), ", ")) CROSSREFS Cf. A000010, A007913, A008683, A008966, A070237. Sequence in context: A165476 A165596 A226523 * A062157 A103131 A112347 Adjacent sequences:  A070235 A070236 A070237 * A070239 A070240 A070241 KEYWORD easy,sign AUTHOR Benoit Cloitre, May 08 2002 EXTENSIONS Comment section edited by Antti Karttunen, Nov 18 2017 STATUS approved

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Last modified May 31 00:29 EDT 2020. Contains 334747 sequences. (Running on oeis4.)