21. (3 points) A workshop originally had no less than 63 workers. On a certain day before the end of January, several workers were transferred in, and thereafter, one additional worker was added to the workshop every day. It is known that the workshop produced a total of 1994 pieces in January, with each worker producing one piece per day. Try to determine: On which day of January did the transfer of workers begin? How many workers were transferred in total?
【Solution】Solution: Since the original number of workers is no less than 63, and
$$
\begin{array}{l}
1994=63 \times 31+41, \\
1994=64 \times 31+10, \\
199441 \text {. }
$$

Upon verification, when $n=2$, $x=20$, and we have:
$$
20+21=41 ;
$$

When $n=4$, $x=1$, and we have:
$$
1+2+3+4=10 \text {. }
$$

Answer: Workers started to be transferred in from January 30, with a total of 21 workers transferred in; or from January 28, with a total of 4 workers transferred in.