OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
FORMULA
a(n)=n*a(n-1)-(n-1)(n-2)/2 with a(1)=2. a(n)=b(1)+b(2)+...+b(n) with b(n) as in A067352.
E.g.f. (with a(0)=2): (exp(x)*(x^2-2*x+2)-6)/(2*(x-1)). - Vaclav Kotesovec, Oct 21 2012
EXAMPLE
The sets begin {1,2},{3,4},{5,6,...,9,10,11},{12,13,...,38,39,40,41},...
MATHEMATICA
Rest[CoefficientList[Series[(E^x*(x^2-2*x+2)-6)/(2*(x-1)), {x, 0, 20}], x]*Range[0, 20]!] (* Vaclav Kotesovec, Oct 21 2012 *)
PROG
(PARI) x='x+O('x^66); Vec(serlaplace((exp(x)*(x^2-2*x+2)-6)/(2*(x-1))) -2 ) \\ Joerg Arndt, May 06 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Floor van Lamoen, Jan 17 2002
EXTENSIONS
More terms from Vincenzo Librandi, May 06 2013
STATUS
approved