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 A070549 a(n) = Card(k 0
 0, 1, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 11, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 14, 15, 16, 16, 16, 16, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 19, 19, 20, 20, 20, 20, 20, 21, 22, 22, 22, 23, 24, 24, 25, 25, 25, 25, 25, 26 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS mu(k)=-1 if k is the product of an odd number of distinct primes. See A057627 for mu(k)=0. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE ListTools:-PartialSums([seq(-min(numtheory:-mobius(n), 0), n=1..100)]); # Robert Israel, Jan 08 2018 MATHEMATICA a[n_]:=Sum[Boole[MoebiusMu[k]==-1], {k, n}]; Array[a, 78] (* Stefano Spezia, Jan 30 2023 *) PROG (PARI) for(n=1, 150, print1(sum(i=1, n, if(moebius(i)+1, 0, 1)), ", ")) CROSSREFS Cf. A008683, A057627. Partial sums of A252233. Sequence in context: A366033 A000720 A230980 * A255574 A283992 A074796 Adjacent sequences: A070546 A070547 A070548 * A070550 A070551 A070552 KEYWORD easy,nonn AUTHOR Benoit Cloitre, May 02 2002 STATUS approved

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Last modified September 30 02:05 EDT 2023. Contains 365781 sequences. (Running on oeis4.)