OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..200
FORMULA
a(n) = n!+4*floor(e*n!)-4, n>0. [Gary Detlefs, Jun 06 2010]
From Robert Israel, May 22 2016: (Start)
a(n) = n!*(1 + Sum_{k=0..n-1} 4/k!) = n! + 4 e n Gamma(n,1).
E.g.f.: (1+4*x*exp(x))/(1-x). (End)
MAPLE
f:= gfun:-rectoproc({a(n)=n*(a(n-1)+4), a(0)=1}, a(n), remember):
map(f, [$0..30]); # Robert Israel, May 22 2016
MATHEMATICA
FoldList[#1*#2 + 4 #2 &, 1, Range[19]] (* Robert G. Wilson v, Jul 07 2012 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Philippe Deléham, Oct 18 2009
STATUS
approved