How to best grab a chunk of Ids from a sequence

I have a process that will be creating a large number of records (about
4Million).  I am thinking of making this process run quicker by writing the
records to a file in 'dump' format and then running that file through psql.

The problem is each record has a sequence number and I need to know the
sequence ids for other
purposes in this process.

My question is is there a way to grab 4 million IDs from a sequence without
calling nextval once for each ID.  Note, this sequence is being actively
drawn on by other processes.

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Bryan White