Shifts left by 3 places under series reversion.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =-1a(5) =1a(6) =-1a(7) =3a(8) =-15a(9) =59a(10) =-189a(11) =567a(12) =-1863a(13) =7141a(14) =-29817a(15) =125919a(16) =-528329a(17) =2238303a(18) =-9769917a(19) =44312225a(20) =-208177669a(21) =1005840685a(22) =-4972561375a(23) =25105651267a(24) =-129470605611a(25) =682486916465