Position of n-th 3 in A031057.

Terms

a(0) =2a(1) =8a(2) =16a(3) =21a(4) =23a(5) =24a(6) =25a(7) =27a(8) =32a(9) =40a(10) =48a(11) =56a(12) =66a(13) =78a(14) =90a(15) =98a(16) =101a(17) =102a(18) =104a(19) =107a(20) =114a(21) =126a(22) =138a(23) =150a(24) =162a(25) =174a(26) =186a(27) =194a(28) =197a(29) =198