What is the reverse (binary) bit number? So you are given a POSITIVE base 10 (decimal) number. Your job is to reverse the binary digits and return that base 10 number. 

Examples:

1 =&gt; 1 (1 =&gt; 1)
2 =&gt; 1 (10 =&gt; 01)
3 =&gt; 3 (11 =&gt; 11)
4 =&gt; 1 (100 =&gt; 001)
5 =&gt; 5 (101 =&gt; 101)
6 =&gt; 3 (110 =&gt; 011)
7 =&gt; 7 (111 =&gt; 111)
8 =&gt; 1 (1000 =&gt; 0001)
9 =&gt; 9 (1001 =&gt; 1001)
10 =&gt; 5 (1010 =&gt; 0101)


This is a code-golf challenge, so the solution that uses the least bytes wins.

This is A030101 in the OEIS.
Python, 29 bytes

lambda n:int(bin(n)[:1:-1],2)


Try it online!

This is an anonymous, unnamed function which returns the result. 



First, bin(n) converts the argument to a binary string. We would ordinarily reverse this with the slice notation [::-1]. This reads the string with a step of -1, i.e. backwards. However, binary strings in Python are prefixed with an 0b, and therefore we give the slicing's second argument as 1, telling Python to read backwards terminating at index 1, thus not reading indexes 1 and 0.

Now that we have the backwards binary string, we pass it to int(...) with the second argument as 2. This reads the string as a base 2 integer, which is then implicity returned by the lambda expression.