3.1. Philatelist Andrey decided to distribute all his stamps equally into 2 envelopes, but it turned out that one stamp was left over. When he distributed them equally into 3 envelopes, one stamp was again left over; when he distributed them equally into 5 envelopes, 3 stamps were left over; finally, when he tried to distribute them equally into 9 envelopes, 7 stamps were left over. How many stamps does Andrey have in total, if recently, to accommodate them all, he had to buy a second album for 150 stamps, as one such album was no longer sufficient?
Answer: 223.

Solution. If the desired number is $x$, then from the first sentence it follows that $x$ is odd, and from the rest it follows that the number $x+2$ must be divisible by 3, 5, and 9, i.e., has the form $5 \cdot 9 \cdot p$. Therefore, $x=45(2 k-1)-2=90 k-47$. According to the condition $150<x \leqslant 300$, so $k=3$. Therefore, $x=223$.