G.f. satisfies A(x) = 1 + x*cycle_index(Klein_4_group, A(x)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =8a(5) =27a(6) =79a(7) =270a(8) =894a(9) =3130a(10) =11011a(11) =39622a(12) =143879a(13) =528919a(14) =1960248a(15) =7323999a(16) =27542451a(17) =104194485a(18) =396204388a(19) =1513599583a(20) =5806283770a(21) =22356914550a(22) =86376741339a(23) =334752355281