a(n) is the first number with a total of exactly n 4's in the decimal digits of its divisors.

Terms

a(0) =1a(1) =4a(2) =24a(3) =44a(4) =84a(5) =144a(6) =336a(7) =432a(8) =720a(9) =840a(10) =1764a(11) =1440a(12) =1344a(13) =2688a(14) =4464a(15) =4488a(16) =4032a(17) =9744a(18) =8064a(19) =6720a(20) =10080a(21) =9240a(22) =17136a(23) =18720a(24) =17472a(25) =13440a(26) =24480a(27) =20160a(28) =28224a(29) =29568