n is equal to the number of 5s in all numbers <= n written in base 7.

Terms

a(0) =761664a(1) =817499a(2) =817500a(3) =817507a(4) =817508a(5) =819609a(6) =823543a(7) =1585207a(8) =1641042a(9) =1641043a(10) =1641050a(11) =1641051a(12) =1643152a(13) =1647086a(14) =2408750a(15) =2464585a(16) =2464586a(17) =2464593a(18) =2464594a(19) =2466695a(20) =2470629a(21) =3232293a(22) =3288128a(23) =3288129a(24) =3288136a(25) =3288137a(26) =3290238a(27) =3294172a(28) =4055836a(29) =4111671