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| n | a(n) |
|---|---|
| 1 | 7 |
| 2 | 47 |
| 3 | 4447 |
| 4 | 7477 |
| 5 | 44777 |
| 6 | 47777 |
| 7 | 74747 |
| 8 | 77447 |
| 9 | 77477 |
| 10 | 77747 |
| 11 | 4444747 |
| 12 | 4447747 |
| 13 | 4747747 |
| 14 | 4774477 |
| 15 | 4774747 |
| 16 | 7444477 |
| 17 | 7447777 |
| 18 | 7474477 |
| 19 | 7477777 |
| 20 | 7747477 |
| 21 | 7774777 |
| 22 | 7777447 |
| 23 | 44447747 |
| 24 | 44747447 |
| 25 | 44747777 |
| 26 | 44774777 |
| 27 | 47447747 |
| 28 | 47774477 |
| 29 | 47774747 |
[7,47,4447,7477,44777,47777,74747,77447,77477, 77747,4444747,4447747,4747747,4774477,4774747, 7444477,7447777,7474477,7477777,7747477,7774777, 7777447,44447747,44747447,44747777,44774777, 47447747,47774477,47774747] |