R_r recurrence even simpler than S_r

[Karol PENSON]

Dear Seqfans,I have a question related to my investigations of some 
integer sequences: 

 Do you know, or do you know how to obtain in closed form the exponential 
generating function of the Hermite polynomials whose order is a multiple 
of three, i.e. I am looking for , im Maple notation:

       sum(t^n*HermiteH(3*n,x)/n!,n=0..infinity)=  ????


 Thanks in advance for the infos.      Karol A. Penson
_________________________________________________________________________
Karol A. PENSON
Universite Paris 6              |  Internet : penson at lptl.jussieu.fr.
Lab. Physique Theorique des     |
Liquides                        | http://www.lptl.jussieu.fr/users/penson
4, place Jussieu, Tour 16, Et. 5|      Tel : (33 1) 44 27 72 33
75252 Paris Cedex 05, France    |      Fax : (33 1) 44 27 51 00