7. The "Hua Luogeng" Golden Cup Junior Mathematics Invitational Competition, the first session was held in 1986, the second session in 1988, the third session in 1991, and thereafter every 2 years. The sum of the digits of the year in which the first "Hua Cup Competition" was held is: $A 1=1+9+8+6=24$.
The sum of the digits of the years in which the first two sessions were held is: $A 2=1+9+8+6+1+9+8+8=50$. 
What is the sum of the digits of the years in which the first 50 sessions of the "Hua Cup Competition" were held, $A 50=$?
7.【Solution】According to the given pattern, among the first 50 editions, there were 7 competitions in the 20th century and 43 competitions in the 21st century.

In the 20th century, it is known that $\mathrm{A} 2=50$, and the sum of the digits of the years for the remaining 5 editions is: $5 \times(1+9$
$$
+9)+(1+3+5+7+9)=95+25=120
$$

Thus, $\mathrm{A}_{7}=\mathrm{A}_{2}+120=170$
In the 21st century, the sum of the digits of the years for the first 45 editions is: $2 \times 45+(1+2+3+\cdots+8) \times 5$
$$
+(1+3+5+7+9) \times 9=495,
$$

The sum of the digits of the years for the first 43 editions is: $495-2-8-7-2-8-9=459$
Therefore, $A_{50}=170+459=629$.