3. (6 points) Among the prime numbers less than 30, those that become multiples of 4 when 3 is added are $\qquad$
【Analysis】According to the definition of prime numbers, a natural number that has only 1 and itself as factors is called a prime number. Prime numbers within 30 are: $2,3,5,7,11,13,17,19,23,29 ; 4$'s multiple characteristic is that the number in the unit's place is even; thus, the solution follows.

【Solution】Solution: $5+3=8$;
$$
\begin{array}{l}
13+3=16 ; \\
17+3=20 ; \\
29+3=32 ;
\end{array}
$$
$8,16,20,32$ are all multiples of 4;
Therefore, the answer is: $5,13,17,29$.