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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 2 |
| 3 | 31 |
| 4 | 20 |
| 5 | 154 |
| 6 | 284 |
| 7 | 1109 |
| 8 | 3472 |
| 9 | 12763 |
| 10 | 48721 |
| 11 | 190256 |
| 12 | 770983 |
| 13 | 3134572 |
| 14 | 12931018 |
| 15 | 53433431 |
| 16 | 221779682 |
| 17 | 921445395 |
| 18 | 3833216521 |
| 19 | 15953742306 |
| 20 | 66423173327 |
| 21 | 276603513242 |
| 22 | 1151978426752 |
| 23 | 4797997758989 |
| 24 | 19984422198978 |
| 25 | 83240190604547 |
[4,2,31,20,154,284,1109,3472,12763,48721,190256, 770983,3134572,12931018,53433431,221779682, 921445395,3833216521,15953742306,66423173327, 276603513242,1151978426752,4797997758989, 19984422198978,83240190604547] |