Numbers whose base-4 representation contains exactly three 1's and three 3's.

Terms

a(0) =1407a(1) =1503a(2) =1527a(3) =1533a(4) =1887a(5) =1911a(6) =1917a(7) =2007a(8) =2013a(9) =2037a(10) =3423a(11) =3447a(12) =3453a(13) =3543a(14) =3549a(15) =3573a(16) =3927a(17) =3933a(18) =3957a(19) =4053a(20) =4479a(21) =4575a(22) =4599a(23) =4605a(24) =4959a(25) =4983a(26) =4989a(27) =5079a(28) =5085a(29) =5109