Thank you for your reply.
I think I don't have the permission to access the Database Shell, it should be in the hands of our PTC distributor (that I will contact later to tell him your response).
In fact, I tried to set the script in the xml file as you wrote me (but with our default "SMBNumberGenerator", here below) but it does not work...it begins with prt0001...
<AttrValuefinal="false" force="false" ignore="false" algorithm="com.ptc.smb.helper.SMBNumberGenerator" id="number"><Arg>15</Arg><Arg>{GEN:wt.enterprise.SequenceGenerator:EPM_seq15:4:0}</Arg></AttrValue>