If you mean the binary encoding based on De Bruijn indices discussed in the Wikipedia, that's actually quite simple. You first need to do De Bruijn encoding, which means replacing the variables with natural numbers denoting the number of λ binders between the variable and its λ binder. In this notation,
λa.λb.λc.(a ((b c) d))
becomes
λλλ 3 ((2 1) d)
where d is some natural number >=4. Since it is unbound in the expression, we can't really tell which number it should be.
Then the encoding itself, defined recursively as
enc(λM) = 00 + enc(M)
enc(MN) = 01 + enc(M) + enc(N)
enc(i) = 1*i + 0
where +
denotes string concatenation and * means repetition. Systematically applying this, we get
enc(λλλ 3 ((2 1) d))
= 00 + enc(λλ 3 ((2 1) d))
= 00 + 00 + enc(λ 3 ((2 1) d))
= 00 + 00 + 00 + enc(3 ((2 1) d))
= 00 + 00 + 00 + 01 + enc(3) + enc((2 1) d)
= 00 + 00 + 00 + 01 + enc(3) + 01 + enc(2 1) + enc(d)
= 00 + 00 + 00 + 01 + enc(3) + 01 + 01 + enc(2) + enc(1) + enc(d)
= 000000011110010111010 + enc(d)
and as you can see, the open parentheses are encoded as 01
while the close parens are not needed in this encoding.