Ailm, Eadha, Idho, Onn, Uath

number 0 : [consonant] H : Uath, the aspirate that precedes or follows some initial or cardinal letters.  The aspirate is often silent, and often unexpressed in letters.  Thus, the aspirate stands for vacuity, or the stillness of a pause in speech, from which all sounds emerge.

number 1 : A : Ailm, as in ABC, Ailm (1), Beith (5), Coll (9).  Cf. A.B.C.D.
number 2 : E : Eadha.  Cf. E.F.G.
number 3 : I : Idho.  Cf. I.J.K.L.M.N.
number 4 : O : Onn.  Cf. O.P.Q.R.S.T.
number 5 : [vowel] U : Uath, equivalent to the consonant H, or Uath (0).  Cf. U.V.W.X.Y.Z.