a(n)=least k such that the base 5 representation of n begins at s(k), where s=A031269.

Terms

a(0) =1a(1) =2a(2) =3a(3) =10a(4) =4a(5) =11a(6) =1a(7) =6a(8) =13a(9) =35a(10) =15a(11) =40a(12) =2a(13) =19a(14) =29a(15) =3a(16) =7a(17) =28a(18) =9a(19) =47a(20) =10a(21) =14a(22) =88a(23) =33a(24) =95a(25) =4a(26) =149a(27) =16a(28) =142a(29) =69