74. There are $n$ pairwise distinct natural numbers, the sum of the products of these numbers taken two at a time is 239, then the maximum value of $n$ is
Answer: 7
Solution: If $n \geq 8$,
then the sum of pairwise products $\geq 0 \times(1+2+3+4+5+6+7)+1 \times(2+3+4+5+6+7)$
$$
+2 \times(3+4+5+6+7)+3 \times(4+5+6+7)+4 \times(5+6+7)+5 \times(6+7)+6 \times 7
$$
$=27+50+66+72+65+42=322$ contradiction
Therefore,
$$
n \leq 7,
$$

Then construct 7 numbers $0,1,2,3,4,6,9$ that satisfy the condition,
so
$n$'s maximum possible value is 7.