OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..50
Eric Weisstein's World of Mathematics, Transposition Graph
Eric Weisstein's World of Mathematics, Wiener Index
FORMULA
From Andrew Howroyd, Sep 08 2017: (Start)
a(n) = n! * A067318(n) / 2.
a(n) = n! * (n*n! - abs(Stirling1(n+1, 2))) / 2.
(End)
a(n) = (n!/2) * Sum_{k=1..n-1} abs(Stirling1(n, n-k))*k. - Andrew Howroyd, Dec 09 2017
MATHEMATICA
Table[n! (n n! + (-1)^n StirlingS1[n + 1, 2])/2, {n, 20}]
PROG
(PARI)
a(n) = n! * (n*n! - abs(stirling(n+1, 2, 1))) / 2; \\ Andrew Howroyd, Sep 08 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Sep 08 2017
EXTENSIONS
Terms a(9) and beyond from Andrew Howroyd, Sep 08 2017
STATUS
approved