The random number system works approximately the same in MPI as normal. -constant_seed and -jran take effect on the head node (if you specified no random number, it would have used the same random number as in non-MPI mode).
The slave nodes add their processor rank to the head node. So, head node seed is 10000, node one uses 10001, node 2 uses 10002, etc.
Running a single-processor job on the seed of a slave node should produce the same trajectory as the slave node did, if the inputs match. This is unlikely to work if you have more than one input being distributed by the head node (since only some jobs would have gone to that particular slave).
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