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
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Dec 07 2017
EXTENSIONS
Terms a(9) and beyond from Andrew Howroyd, Dec 09 2017
STATUS
approved