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A296194
Harary index of the n-transposition graph.
2
0, 1, 12, 162, 3010, 81000, 3105396, 162469104, 11117235312, 961808277600, 102496397652000, 13180200302839680, 2011319092988899200, 359224661189539192320, 74214101648670824736000, 17557926151618710547200000, 4715558231100365363023411200
OFFSET
1,3
LINKS
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
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Dec 07 2017
EXTENSIONS
Terms a(9) and beyond from Andrew Howroyd, Dec 09 2017
STATUS
approved