将组放入组中[123[a-u]]

import itertools

result = [''.join(x) for x in itertools.product('123', 'abcdefghijklmnopqrstuvwxyz'[:21])]
print(result)

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> result = new ArrayList<>();
        for (char c = 'a'; c <= 'u'; c++) {
            for (int i = 1; i <= 3; i++) {
                result.add(String.valueOf(i) + c);
            }
        }
        System.out.println(result);
    }
}

const result = [];
for (let i = 1; i <= 3; i++) {
  for (let j = 97; j <= 117; j++) {
    result.push(i + String.fromCharCode(j));
  }
}
console.log(result);