a(n) = A054108(n) + 4*(-1)^n.

Terms

a(0) =1a(1) =19a(2) =51a(3) =201a(4) =723a(5) =2709a(6) =10161a(7) =38459a(8) =146297a(9) =559135a(10) =2145021a(11) =8255579a(12) =31861021a(13) =123256499a(14) =477823891a(15) =1855782329a(16) =7219352971a(17) =28125910829a(18) =109720617991a(19) =428537256449