OFFSET
0,3
COMMENTS
The mean root degree approaches 2 as n -> infinity.
LINKS
Philippe Flajolet and Robert Sedgewick, Analytic Combinatorics, Cambridge Univ. Press, 2009, page 179.
FORMULA
a(n) = Sum_{k=0..n} A206429(n,k)*k.
E.g.f.: T(x)^2 where T(x) is the e.g.f. for A000169.
a(n) = 2*(n^(n-1) - n^(n-2)).
a(n) = 2*A053506(n). - R. J. Mathar, Nov 07 2014
MATHEMATICA
nn=15; t=Sum[n^(n-1)x^n/n!, {n, 1, nn}]; D[ Range[0, nn]!CoefficientList[Series[x Exp[y t], {x, 0, nn}], x], y]/.y->1
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Geoffrey Critzer, Feb 13 2012
EXTENSIONS
a(10) corrected by Georg Fischer, Mar 23 2023
STATUS
approved