Puzzle 6.
A little refactor, for more efficient sum of squares.
Tweaking natural number sequence implementation.
Puzzle 7.  Rewrote prime stream to be more efficient.
Removing unused imports.
Puzzle 8.
Puzzle 9.
Deleting dead code.
Puzzle 10.  Further optimisation of the primes generator.
Puzzle 10.  Further optimisation of primes code, just use Long instead of BigInt.