Odd Motzkin numbers.

Terms

a(0) =1a(1) =1a(2) =9a(3) =21a(4) =51a(5) =127a(6) =323a(7) =835a(8) =15511a(9) =41835a(10) =853467a(11) =2356779a(12) =50852019a(13) =142547559a(14) =400763223a(15) =1129760415a(16) =3192727797a(17) =9043402501a(18) =208023278209a(19) =593742784829