[seqfan] Help with A002793 needed/Karol A. Penson

[Karol PENSON]

Can anyone help with the following three questions concerning A002793:

     1.  is the formula for a(n) known ?
     2.  is any generating function (ogf , egf ... etc. ) of a(n) known ?
     3.  in one of my calculations the following splitting of a(n)'s 
appear :

                   a(2)=4    =3+1
                   a(3)=20  =11+8+1
                   a(4)=124=50+58+15+1
                   a(5)=920=274+444+177+24+1,
                         etc.
         I would be happy to obtain the formula for the triangle.

       Thanks in advance ,    Karol A. Penson