To log in you must have an account. I'm not sure I am permitted to give an exact core count here, but there are 4 clusters in total, and 2 of these have over 320 cores each. There is a smaller one with 24 and the middle one has over 150 cores. However, it's unlikely that you can reserve more than 256 cores for a job, I would say, due to other jobs running. But 64 shouldn't be a big problem, maybe also 128 if you are ok to wait in the queue a bit.