3. Let n be a natural number, then the odd number is (), the even number is (), and the three consecutive natural numbers are（ 3. If n is a natural number, then the odd number is () and the even number is () and the three consecutive natural numbers are () 4. If the chickens and rabbits are in the same cage, m chickens and N rabbits, there are () heads and () feet in total. 5. Greening a piece of land with a 5-person team can be completed in M days. Greening this piece of land with an 8-person team can be completed in () days

3. Let n be a natural number, then the odd number is (), the even number is (), and the three consecutive natural numbers are（ 3. If n is a natural number, then the odd number is () and the even number is () and the three consecutive natural numbers are () 4. If the chickens and rabbits are in the same cage, m chickens and N rabbits, there are () heads and () feet in total. 5. Greening a piece of land with a 5-person team can be completed in M days. Greening this piece of land with an 8-person team can be completed in () days

2n+1
2n