A103828(n) + 1.

Terms

a(0) =2a(1) =4a(2) =10a(3) =28a(4) =70a(5) =430a(6) =1060a(7) =56500a(8) =166840a(9) =5020060a(10) =7681810a(11) =274343590a(12) =8316187180