Irregular triangle in which first row is 1, n-th row (n > 1) lists distinct prime factors of n.

Terms

a(0) =1a(1) =2a(2) =3a(3) =2a(4) =5a(5) =2a(6) =3a(7) =7a(8) =2a(9) =3a(10) =2a(11) =5a(12) =11a(13) =2a(14) =3a(15) =13a(16) =2a(17) =7a(18) =3a(19) =5a(20) =2a(21) =17a(22) =2a(23) =3a(24) =19a(25) =2a(26) =5a(27) =3a(28) =7a(29) =2