G.f.: Sum_{n=-oo..+oo} x^n * (1 - x^n)^(3*n).

Terms

a(0) =1a(1) =1a(2) =-3a(3) =1a(4) =-12a(5) =-9a(6) =-8a(7) =-20a(8) =-59a(9) =1a(10) =-43a(11) =-54a(12) =-101a(13) =-77a(14) =-89a(15) =127a(16) =-307a(17) =-135a(18) =-26a(19) =-170a(20) =73a(21) =85a(22) =199a(23) =-252a(24) =-888a(25) =1066a(26) =924a(27) =1a(28) =1177a(29) =-405