A numerical sequence was a sequence used as communication including information such as stellar locations.

While Doctor Phlox was briefly part of the Borg Collective hive mind in 2153, he was able to hear a subspace message including a numerical sequence sent from the Borg drones in the Alpha Quadrant to their homeworld in the Delta Quadrant. The information were pulsar frequencies depicting the location of Earth. (ENT: "Regeneration")

In 2376, the astronomer on Kelemane's planet was sending radio waves with prime numbers in a numerical sequence to the "Sky Ship", the USS Voyager. (VOY: "Blink of an Eye")