The latest Pledge number is stored in a Sequence (an Oracle db object) called PLG_NUMBER_SEQ and it is incremented as it is used in Batch Detail or other places where a new Pledge number is required. Here is an example of the settings for ARC4:
-- Create sequence Arc4
create sequence PBDS.PLG_NUMBER_SEQ
start with 61
increment by 1
1. The maxvalue controls the highest value a pledge number can go. Typically, this value can run up to 999999999 or such that will yield non-repeating values.
2. The cycle parameter has been turned on in this example, which means that once it gets to the max number, it starts again from the beginning.