A signed variant of the Motzkin numbers.

Terms

a(0) =1a(1) =1a(2) =-1a(3) =2a(4) =-4a(5) =9a(6) =-21a(7) =51a(8) =-127a(9) =323a(10) =-835a(11) =2188a(12) =-5798a(13) =15511a(14) =-41835a(15) =113634a(16) =-310572a(17) =853467a(18) =-2356779a(19) =6536382a(20) =-18199284a(21) =50852019a(22) =-142547559a(23) =400763223a(24) =-1129760415a(25) =3192727797a(26) =-9043402501a(27) =25669818476a(28) =-73007772802a(29) =208023278209