A296194 Harary index of the n-transposition graph.

0, 1, 12, 162, 3010, 81000, 3105396, 162469104, 11117235312, 961808277600, 102496397652000, 13180200302839680, 2011319092988899200, 359224661189539192320, 74214101648670824736000, 17557926151618710547200000, 4715558231100365363023411200

Offset

1,3

Links

Andrew Howroyd, Table of n, a(n) for n = 1..100

Eric Weisstein's World of Mathematics, Harary Index

Eric Weisstein's World of Mathematics, Transposition Graph

Formula

a(n) = (n!/2) * Sum_{k=1..n-1} abs(Stirling1(n, n-k))/k. - Andrew Howroyd, Dec 09 2017

Mathematica

Table[n! Sum[((-1)^k StirlingS1[n, n - k])/k, {k, n - 1}]/2, {n, 20}]

Prog

(PARI) a(n)={n!*sum(k=1, n-1, abs(stirling(n, n-k, 1))/k)/2} \\ Andrew Howroyd, Dec 09 2017

Crossrefs

Cf. A292062.

Sequence in context: A048603 A275040 A109391 * A307071 A138455 A024221

Adjacent sequences: A296191 A296192 A296193 * A296195 A296196 A296197

Keyword

nonn

Author

Eric W. Weisstein, Dec 07 2017

Extensions

Terms a(9) and beyond from Andrew Howroyd, Dec 09 2017

Status

approved