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A123919
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Number of numbers congruent to 2 or 4 mod 6 and <= n.
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2
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0, 1, 1, 2, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 10, 10, 10, 10, 11, 11, 12, 12, 12, 12, 13, 13, 14, 14, 14, 14, 15, 15, 16, 16, 16, 16, 17, 17, 18, 18, 18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 22, 22, 22, 22, 23, 23, 24, 24, 24, 24, 25, 25, 26, 26, 26
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| First differences of A056827. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 22 2008]
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FORMULA
| G.f.: x^2(1+x^2)/((1+x)(1-x)^2*(1+x+x^2)(1-x+x^2)). a(n+1)-a(n)=A120325(n+1). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 22 2008]
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MATHEMATICA
| f[n_] := Floor[n/2] - Floor[n/6]; Array[f, 78] (* Robert G. Wilson v Oct 29 2006 *)
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CROSSREFS
| Cf. A047235.
Sequence in context: A189671 A109497 A156078 * A194324 A194328 A194304
Adjacent sequences: A123916 A123917 A123918 * A123920 A123921 A123922
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KEYWORD
| easy,nonn
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AUTHOR
| Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Oct 29 2006
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