19. (3 points) Teacher Wang wrote several consecutive natural numbers starting from 1 on the blackboard: $1,2,3,4, \cdots$, and then erased three numbers (two of which are prime numbers). If the average of the remaining numbers is $19 \frac{8}{9}$, then the total number of numbers Teacher Wang wrote on the blackboard is $\qquad$, and the maximum sum of the two prime numbers erased is $\qquad$.

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【Solution】Solution: Given that the average of the remaining numbers is $19 \frac{8}{9}$,
it implies that the largest number is approximately $20 \times 2=40$,
and knowing that the denominator is 9, the number of remaining numbers must be a multiple of 9, thus we deduce that there are 36 remaining numbers.
Originally, the numbers from 1 to 39, a total of 39 numbers, were written;
The sum of the remaining 36 numbers: $19 \frac{8}{9} \times 36=716$,
The total sum of the 39 numbers: $(1+39) \times 39 \div 2=780$,
The sum of the three erased numbers: $780-716=64$,
According to the problem, we deduce that the smallest of the three erased numbers is 1,
Then the sum of the two prime numbers $63=61+2$ can be valid,
$61>39$ is not valid;
If the other erased number is the smallest composite number 4,
$64-4=60$
$60=29+31=23+37$, valid;
In summary, the maximum sum of the two erased prime numbers is 60.
Therefore, the answer is: 39,60.