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
Links
- Eric Weisstein's World of Mathematics, Harary Index
- Eric Weisstein's World of Mathematics, Permutation Star Graph
Programs
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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 *)