Find the rules and write the formula: 1 + 2,2 + 4,3 + 6,4 + 8,1 + 10,2 + 12,3 + 14,4 + 16,1 + 18. What's the formula 2001? Hurry, please, wait online for half an hour~~~~~~~~~·

Find the rules and write the formula: 1 + 2,2 + 4,3 + 6,4 + 8,1 + 10,2 + 12,3 + 14,4 + 16,1 + 18. What's the formula 2001? Hurry, please, wait online for half an hour~~~~~~~~~·

solution
We can see four cycles
In April of 2001, more than 1 is 1 + XX
If you look at the next digit, you can see that adding 2 one by one, the next digit of the nth formula is 2n
We can get 1 + 4002