login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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
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: A118413 A295320 A093419 * A096620 A331124 A299209
KEYWORD
nonn,frac
AUTHOR
Eric W. Weisstein, Apr 30 2009
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 24 11:50 EDT 2024. Contains 373677 sequences. (Running on oeis4.)