euler: Simplify problem 15

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>
euler: Simplify problem 16

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>
euler: Simplify problem 20

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>
euler: Simplify problem 30

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>
euler: Simplify problem 34

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>
euler: Simplify problem 48

Signed-off-by: Aleksi Pitkäjärvi <aleksi.pitkajarvi@valotrading.com>