A296057 Denominators of Harary index for the n-permutation star graph.

1, 1, 1, 1, 1, 1, 1, 1, 11, 143, 13, 13, 17, 19, 323, 323, 437, 437, 23, 1, 667, 20677, 899, 31, 899, 33263, 33263, 33263, 47027, 2022161, 65231, 65231, 3065857, 3065857, 3065857, 3065857, 4391633, 4391633, 4391633, 4391633, 6319667, 385499687, 8965109, 8965109

Offset

1,9

Links

Table of n, a(n) for n=1..44.

Eric Weisstein's World of Mathematics, Harary Index

Eric Weisstein's World of Mathematics, Permutation Star Graph

Mathematica

A007799[n_, i_] := Sum[Binomial[n - 1, k] Binomial[n - 1 - k, t] StirlingS1[k + 1, i - k + 1 - 2 t] (-1)^(i + 2 - t), {k, 0, Min[n - 1, i + 1]}, {t, Max[0, Ceiling[(i - 2 k)/2]], Min[n - 1 - k, Floor[(i + 1 - k)/2]]}];
Table[n! Sum[A007799[n, k]/k, {k, Floor[3 (n - 1)/2]}]/2, {n, 20}] // Denominator (* Eric W. Weisstein, Dec 09 2017 *)

Crossrefs

Cf. A296190 (numerators), A007799, A284039.

Sequence in context: A293988 A024141 A289216 * A323029 A221580 A024140

Adjacent sequences: A296054 A296055 A296056 * A296058 A296059 A296060

Keyword

nonn,frac

Author

Andrew Howroyd, Dec 09 2017

Status

approved