From expansion of Belyi function for octahedron.

Terms

a(0) =1a(1) =-46a(2) =769a(3) =-5632a(4) =18688a(5) =-44032a(6) =85760a(7) =-147968a(8) =234752a(9) =-350208a(10) =498432a(11) =-683520a(12) =909568a(13) =-1180672a(14) =1500928a(15) =-1874432a(16) =2305280a(17) =-2797568a(18) =3355392a(19) =-3982848a(20) =4684032a(21) =-5463040a(22) =6323968a(23) =-7270912a(24) =8307968a(25) =-9439232a(26) =10668800a(27) =-12000768a(28) =13439232a(29) =-14988288