4. Xiaoming constructed a sequence using the digits $2$, $0$, $1$, $6$ (continuously appending these four digits in this order to the end of the number): 2, 20, 201, 2016, 20162, 201620, 2016201, 20162016, 201620162, … In this sequence, the number of prime numbers is $\qquad$
【Analysis】In this sequence, the numbers follow a cycle with the units digit being $2, 0, 1, 6$, which means that except for the units digit being 1, the rest are even numbers. Among even numbers, only 2 is a prime number, so the first number in the sequence is a prime number, and the rest of the even numbers are not prime numbers.
Next, consider the odd numbers ending in 1. The sum of the digits of these numbers is $(2+0+1+6 \times) k+2+0+1=9 k+3$ (where $k$ is a natural number), so these numbers must be multiples of 3, and none of these numbers are 3, so these numbers are not prime numbers.
In summary, there is only 1 prime number.