a(n)=least k such that base 4 representation of n begins at s(k), where s=A030401.

Terms

a(0) =1a(1) =7a(2) =2a(3) =15a(4) =3a(5) =8a(6) =1a(7) =39a(8) =7a(9) =51a(10) =9a(11) =63a(12) =2a(13) =6a(14) =10a(15) =87a(16) =15a(17) =103a(18) =18a(19) =17a(20) =3a(21) =29a(22) =4a(23) =41a(24) =27a(25) =53a(26) =8a(27) =65a(28) =1a(29) =5