G.f. satisfies A(x) = exp( Sum_{k>=1} A(x^k) * x^k/(k * (1 + 3*x^k)) ).

Terms

a(0) =1a(1) =1a(2) =-1a(3) =4a(4) =-6a(5) =11a(6) =-22a(7) =62a(8) =-151a(9) =353a(10) =-867a(11) =2261a(12) =-5861a(13) =15178a(14) =-39878a(15) =106099a(16) =-283823a(17) =763248a(18) =-2065453a(19) =5621318a(20) =-15368682a(21) =42190539a(22) =-116281176a(23) =321647511a(24) =-892617214a(25) =2484583934a(26) =-6935203356a(27) =19408586888a(28) =-54447145335a(29) =153084848495