Answer
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LHK - or Last Hunk Key tells DNs to hunt (when busy) to the next KEY number.

Your DNs must be MARP on your TN

LHK: n - The key number of the last DN key that should be included in a "Hunt up to the next key" scenario

• LHK 1 means calls will hunt up the keys from KEY 0 to KEY 1.
• LHK 20 means any DN Keys from 00 to 20 that are in a group (KEY 2, 3, 4 or KEY 15, 16, 17, 18, 19, 20) will hunt from one to the next.
• DNs must be in a series with no spaces to be part of a Last Hunt Key group.
• There must be a value in the HUNT prompt in order to be prompted for LHK.  Using HUNT 000 is how to get to LHK without specifying another DN in HUNT.

Examples:

This telephone has HUNT 000 and LHK 1.  If 1034 is busy, the next call will go to 1005.  If 1034 and 1005 are busy, callers will get a busy signal.

The following telephone has HUNT 3000 and LHK 5.  If 1172 is busy, the next call will go to 1132.  If 1172 and 1132 are busy, the next call will go to 3000. 

Callers dialing 2122 will hunt to 2157, then to 2188, then to HUNT 3000.  Note that any blank or feature key breaks the series of hunting.

Link to this page: http://www.ghtrout.net/rdr/lhk.html