A vector used internally to produce `#N=' labels and `#N#' references.
The Lisp printer uses this vector to detect Lisp objects referenced more
When you bind `print-continuous-numbering' to t, you should probably
also bind `print-number-table' to nil. This ensures that the value of
`print-number-table' can be garbage-collected once the printing is
done. If all elements of `print-number-table' are nil, it means that
the printing done so far has not found any shared structure or objects
that need to be recorded in the table.