2*n analog to Keith numbers.

Terms

a(0) =5a(1) =9a(2) =10a(3) =15a(4) =19a(5) =20a(6) =25a(7) =28a(8) =30a(9) =35a(10) =40a(11) =45a(12) =47a(13) =66a(14) =88a(15) =132a(16) =198a(17) =2006a(18) =2740a(19) =4012a(20) =4419a(21) =13635a(22) =56357a(23) =338540a(24) =354164a(25) =419966a(26) =441972a(27) =685704a(28) =803678a(29) =1528803