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A160049 Denominator of the Harary number for the path graph P_n. 2
1, 1, 1, 3, 6, 5, 10, 35, 140, 126, 1260, 1155, 13860, 12870, 12012, 45045, 360360, 340340, 2042040, 1939938, 369512, 117572, 2586584, 7436429, 178474296, 171609900, 1487285800, 1434168450, 40156716600, 38818159380, 1164544781400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Is this the same as A096620? - R. J. Mathar, Jan 26 2010

Yes, except for offset, because n*(harmonic(n)-harmonic(n-1)) = 1 which is an integer. - Andrew Howroyd, Oct 31 2017

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200

Eric Weisstein's World of Mathematics, Harary Index

Eric Weisstein's World of Mathematics, Harmonic Number

EXAMPLE

0, 2, 5, 26/3, 77/6, 87/5, 223/10, 962/35, 4609/140, 4861/126, ...

PROG

(PARI)

harmonic(n)=sum(k=1, n, 1/k);

a(n)=denominator(2*n*harmonic(n)); \\ Andrew Howroyd, Oct 31 2017

CROSSREFS

Cf. A160048.

Sequence in context: A295320 A096620 A093419 * A299209 A007479 A076535

Adjacent sequences:  A160046 A160047 A160048 * A160050 A160051 A160052

KEYWORD

nonn,frac

AUTHOR

Eric W. Weisstein, Apr 30 2009

STATUS

approved

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Last modified November 17 18:24 EST 2018. Contains 317276 sequences. (Running on oeis4.)