Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Class | Type | No. built (Converted*) | Year built (Converted*) | No. range | Withdrawn |
| --- | --- | --- | --- | --- | --- |
| Class 420 | 4Big | 18 | 1965-66 | 7031-7048 | 1986.0 |
| Class 420 | 4Big | 10 | 1970 | 7049-7058 | 1988.0 |
| Class 421 | 4Cig | 36 | 1963-66 | 7301-7336 (later 1101-1136) | 1993.0 |
| Class 421 | 4Cig | 102 | 1970-74 | 7337-7438 (later 1201-1300) | 1993.0 |
| Class 421 | 8Mig | 2* | 1983* | 2601–2602 | 1983.0 |
Question:
Tell me the number range for 1965-66
Answer:
7031-7048