Inverse of number triangle binomial(3n-k,n-k).

Terms

a(0) =1a(1) =-3a(2) =1a(3) =0a(4) =-5a(5) =1a(6) =0a(7) =7a(8) =-7a(9) =1a(10) =0a(11) =-3a(12) =18a(13) =-9a(14) =1a(15) =0a(16) =0a(17) =-22a(18) =33a(19) =-11a(20) =1a(21) =0a(22) =0a(23) =13a(24) =-65a(25) =52a(26) =-13a(27) =1a(28) =0a(29) =0