a(n) = least k such that base 5 representation of n begins at s(k), where s = A031219.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =7a(6) =1a(7) =11a(8) =13a(9) =15a(10) =10a(11) =19a(12) =2a(13) =23a(14) =25a(15) =12a(16) =22a(17) =31a(18) =3a(19) =35a(20) =4a(21) =14a(22) =24a(23) =34a(24) =45a(25) =5a(26) =51a(27) =54a(28) =57a(29) =50