Decimal encoding of the prime factorization of n: concatenation of prime factors and exponents.

Terms

a(0) =21a(1) =31a(2) =22a(3) =51a(4) =2131a(5) =71a(6) =23a(7) =32a(8) =2151a(9) =111a(10) =2231a(11) =131a(12) =2171a(13) =3151a(14) =24a(15) =171a(16) =2132a(17) =191a(18) =2251a(19) =3171a(20) =21111a(21) =231a(22) =2331a(23) =52a(24) =21131a(25) =33a(26) =2271a(27) =291a(28) =213151a(29) =311