|
Search: id:A072663
|
|
|
| A072663 |
|
Numbers n such that sum(k=1,n,(-1)^k*k*floor(n/k)) = 0. |
|
+0
4
|
|
| 2, 26, 28, 76, 210, 1801, 3508, 16180, 29286, 33988, 1161208, 4010473, 164048770
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
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
|
|
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}]
|
|
PROGRAM
|
(PARI) a(n)=sum(k=1, n, (-1)^k*k*floor(n/k))
|
|
CROSSREFS
|
The zeros of A024919.
Sequence in context: A056948 A035420 A022375 this_sequence A050905 A067571 A084298
Adjacent sequences: A072660 A072661 A072662 this_sequence A072664 A072665 A072666
|
|
KEYWORD
|
more,nonn
|
|
AUTHOR
|
Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 10 2002
|
|
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
|
|
|
Search completed in 0.002 seconds
|
