As far as I know, separate is Latin 7, and this is going to be English month again. In fact, separate (now September, also Latin 9) was originally July and oct (now October) means 8.
This reason is about Augustus the Great. Let's not talk so much. Let's solve your problem first.
nil-,un-1,bi-2,tri-3,quad-4,pent-5,hex-6,sept-7,oct-8,enn-9。