Restricted mini challenges Cop's Thread
Haskell, A209229, (cracked)



11 characters (including newline):

s&lt;=[ ]
how!


Outputs True/False as an indicator function for powers of 2:

1 =&gt; True
2 =&gt; True
3 =&gt; False
4 =&gt; True
5 =&gt; False
6 =&gt; False
7 =&gt; False
8 =&gt; True
9 =&gt; False
...


Inputs are positive integers.