In the Pythagorean and Platonic tradition the study of numbers was essential, as witnessed by the large number of treatises on Numbers from the Classical world.
Each of the numbers below 10, and possibly even higher, was considered unique and significant. Where the Hebrew Kabbala has its 10 spheres and their attributes the Greeks gave names and associations to the Numbers.
Here are a few, taken from the excellent Pythagorean Sourcebook by Kenneth Sylvan Guthrie.
1) The Monad: Instrument of Truth; the inn-keeper (that which takes in all); Zeus; God; Prometheus; Not many (A-pollon); A Chariot; A Ship; Essence; Life; Paradigm; Darkness; Harmony; A Friend; Infinite Expanse (Chaos)
2) The Dyad: Inequality; Indefinite; Unlimited; Without form or Figure; Growth; Birth; Judgement; Anguish; That which must be Endured, Misery; Isis; Rhea (Kronos Wife); Selene; Movement; Obstinacy; Nature
3) The Triad: Proportion; Harmonia; Marriage; Hecate; Piety; Good Counsel; The Mean between two Extremes; Mind; Peace; The All
4) The Tetrad: Nature of Change; Hercules; Holding the Key of Nature
5) The Pentad: Alteration; Lack of Strife; Androgeny; Aphrodite; Boubastia 9after Egyptian Boubastis); Wedding; Double; Pallas; Justice; Forethought; Light
6) The Hexad: Resembling Justice; the ThunderStone; Amphitrite (word play Amphis – on both sides, Trias – three); Male-Female; Finest of All; Form of Forms;
7) The Heptad: Forager – epithet of Athena: Athena; Akropolis; The Reaper; Bringing to Completion; The Virgin; Fortune (Fate); Preserving;
8) The Octad: Untimely Born; Seat or Abode; Euterpe; Cadmia; All Harmonious
9) The Ennead: Brother and Consort of Zeus; Hera; Hephaestus; Absence of Strife; Prometheus; Terpsichore; Hyperion; Oceanus; Maiden (Kore); Of the Kouretes; Consort and Brother; Perfection;
10) The Decad: Eternity (Aeon); Untiring; Atlas; Helios; Key-Holding; Cosmos; Ourania; Heavens; Strength; Faith; All; Phanes.
There are others, but from this small collection we gain some idea of the values of each of the Numbers as seen through Classical Greek eyes.