A355906(n)/3.

Terms

a(0) =0a(1) =0a(2) =-1a(3) =1a(4) =-2a(5) =3a(6) =-5a(7) =7a(8) =-11a(9) =16a(10) =-25a(11) =37a(12) =-56a(13) =84a(14) =-127a(15) =190a(16) =-286a(17) =429a(18) =-644a(19) =966