#include "eoslib/print.hpp"  
#include "BigIntegerLibrary.hpp"  

 BigInteger a = 65536;  
 print("a * a * a * a * a * a * a * a: ", ( a * a * a * a * a * a * a * a ) );

then, eosd prints 340282366920938463463374607431768211456.

github: https://github.com/plactal/biginteger-for-eosio