a(n), when spelled in English, is the smallest positive integer with exactly n letters.

Terms

a(0) =1a(1) =4a(2) =3a(3) =11a(4) =15a(5) =13a(6) =17a(7) =24a(8) =23a(9) =73a(10) =101a(11) =104a(12) =103a(13) =111a(14) =115a(15) =113a(16) =117a(17) =124a(18) =123a(19) =173a(20) =323a(21) =373a(22) =1104a(23) =1103a(24) =1111a(25) =1115a(26) =1113a(27) =1117a(28) =1124a(29) =1123