3 added 2 characters in body
source | link

Python 2, 39 3838 34 bytes

f=lambda n:n and f-n%6+1+f(~-n/6)+`-n%6+1`or''*10

Try it online!Try it online!

Outputs 1-indexed number

Python 2, 39 38 bytes

f=lambda n:n and f(~-n/6)+`-n%6+1`or''

Try it online!

Outputs 1-indexed number

Python 2, 39 38 34 bytes

f=lambda n:n and-n%6+1+f(~-n/6)*10

Try it online!

Outputs 1-indexed number

2 deleted 20 characters in body
source | link

Python 2, 3939 38 bytes

f=lambda n:n and f(~-n/6)+`6-~+`-n%6`or''n%6+1`or''

Try it online!Try it online!

Outputs 1-indexed number

Python 2, 39 bytes

f=lambda n:n and f(~-n/6)+`6-~-n%6`or''

Try it online!

Outputs 1-indexed number

Python 2, 39 38 bytes

f=lambda n:n and f(~-n/6)+`-n%6+1`or''

Try it online!

Outputs 1-indexed number

1
source | link

Python 2, 39 bytes

f=lambda n:n and f(~-n/6)+`6-~-n%6`or''

Try it online!

Outputs 1-indexed number