a(n) = concatenation of all (i, e_i) with e_i > 0, when n = Product_{i >= 1} prime(i)^e_i.

Terms

a(0) =0a(1) =11a(2) =21a(3) =12a(4) =31a(5) =1121a(6) =41a(7) =13a(8) =22a(9) =1131a(10) =51a(11) =1221a(12) =61a(13) =1141a(14) =2131a(15) =14a(16) =71a(17) =1122a(18) =81a(19) =1231a(20) =2141a(21) =1151a(22) =91a(23) =1321a(24) =32a(25) =1161a(26) =23a(27) =1241a(28) =101a(29) =112131