Question 973803
<pre>
2^p-1  means {{{2^p-1}}}, no parentheses needs. The other tutor is wrong.]
</pre>
The smallest prime p such that 2^p - 1 is composite.  
<pre>
Let's try to find it.  Hope it's not too large.

{{{2^2-1}}}{{{""=""}}}{{{4-1}}}{{{""=""}}}{{{3}}}{{{matrix(1,3,which,is,"prime.")}}}
{{{2^3-1}}}{{{""=""}}}{{{8-1}}}{{{""=""}}}{{{7}}}{{{matrix(1,3,which,is,"prime.")}}}
{{{2^5-1}}}{{{""=""}}}{{{32-1}}}{{{""=""}}}{{{31}}}{{{matrix(1,3,which,is,"prime.")}}}
{{{2^7-1}}}{{{""=""}}}{{{128-1}}}{{{""=""}}}{{{127}}}{{{matrix(1,3,which,is,"prime.")}}}
{{{2^11-1}}}{{{""=""}}}{{{2048-1}}}{{{""=""}}}{{{2047}}}{{{matrix(1,3,which,is,"23×89.")}}}

That's it! Answer = 11
 
Edwin</pre>