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A072663
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Numbers n such that sum(k=1,n,(-1)^k*k*floor(n/k)) = 0.
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3
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2, 26, 28, 76, 210, 1801, 3508, 16180, 29286, 33988, 1161208, 4010473, 164048770
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| It is easy to see that if a(n)=sum(k=1,n,(-1)^k*k*floor(n/k)) then a(n)=a(n-1)+(2^(L+1)-3)*sigma(M) if n=2^L*M, where M is odd and L>=0. Using this we can get a faster program to calculate the sequence. - Robert Gerbicz (gerbicz(AT)freemail.hu), Aug 30 2002
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MATHEMATICA
| f[n_] := Sum[(-1)^i*i*Floor[n/i], {i, 1, n}]; Do[s = f[n]; If[s == 0, Print[n]], {n, 1, 40000}]
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PROG
| (PARI) a(n)=sum(k=1, n, (-1)^k*k*floor(n/k))
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CROSSREFS
| The zeros of A024919.
Sequence in context: A056948 A035420 A022375 * A050905 A067571 A084298
Adjacent sequences: A072660 A072661 A072662 * A072664 A072665 A072666
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KEYWORD
| more,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 10 2002
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EXTENSIONS
| Four more terms from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 13 2002
More terms from Robert Gerbicz (gerbicz(AT)freemail.hu), Aug 30 2002
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