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A160049 Denominator of the Harary number for the path graph P_n. 2

%I

%S 1,1,1,3,6,5,10,35,140,126,1260,1155,13860,12870,12012,45045,360360,

%T 340340,2042040,1939938,369512,117572,2586584,7436429,178474296,

%U 171609900,1487285800,1434168450,40156716600,38818159380,1164544781400

%N Denominator of the Harary number for the path graph P_n.

%C Is this the same as A096620? - _R. J. Mathar_, Jan 26 2010

%C Yes, except for offset, because n*(harmonic(n)-harmonic(n-1)) = 1 which is an integer. - _Andrew Howroyd_, Oct 31 2017

%H Andrew Howroyd, <a href="/A160049/b160049.txt">Table of n, a(n) for n = 1..200</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HararyIndex.html">Harary Index</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>

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

%o (PARI)

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

%o a(n)=denominator(2*n*harmonic(n)); \\ _Andrew Howroyd_, Oct 31 2017

%Y Cf. A160048.

%K nonn,frac

%O 1,4

%A _Eric W. Weisstein_, Apr 30 2009

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Last modified June 5 12:47 EDT 2020. Contains 334840 sequences. (Running on oeis4.)