a(1) = 11 by convention; for n > 1, if n = p^a*q^b... then a(n) = concatenate(p,a,q,b,...).

Terms

a(0) =11a(1) =21a(2) =31a(3) =22a(4) =51a(5) =2131a(6) =71a(7) =23a(8) =32a(9) =2151a(10) =111a(11) =2231a(12) =131a(13) =2171a(14) =3151a(15) =24a(16) =171a(17) =2132a(18) =191a(19) =2251a(20) =3171a(21) =21111a(22) =231a(23) =2331a(24) =52a(25) =21131a(26) =33a(27) =2271a(28) =291a(29) =213151