Numbers whose base-4 representation contains no 1's and exactly three 2's.

Terms

a(0) =42a(1) =138a(2) =162a(3) =168a(4) =171a(5) =174a(6) =186a(7) =234a(8) =522a(9) =546a(10) =552a(11) =555a(12) =558a(13) =570a(14) =642a(15) =648a(16) =651a(17) =654a(18) =672a(19) =675a(20) =684a(21) =687a(22) =690a(23) =696a(24) =699a(25) =702a(26) =714a(27) =738a(28) =744a(29) =747