A four-digit number is written in a piece of paper. Can you figure it out?

Clues:

1. The second isn't a 6.

2. Only one digit starts with a vowel.

3. The fourth is greater than the first, which is greater than or equal to the third, and is greater than the second.

4. Either the first two numbers are even & the last two numbers are odd or vice versa.

5. The difference between the 1st & 2nd, is the same as the difference between the 4th & 3rd.

6. One of the numbers is prime; three are composite.

Hint: In clue 6, the only prime numbers that have a single digit are 2, 3, 5 and 7.

Hint 2: The only numbers that start with a vowel are 1 and 8.

Hint 3: The second is 4.