Answer:
9404 digits
Explanation:
The numbers written:
51, 53, 55, 57, 59, . . . 97, 99 [5*5=25 numbers; 50 digits]
101, 103, 105, . . . 997, 999 [9*50=450 numbers; 1350 digits]
1001, 1003, 1005, . . . 4997, 4999, 5001 [40*50+1=2001 numbers; 8004 digits]
Total:
50 + 1350 + 8004 = 9404 digits