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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 23 |
| 3 | 168 |
| 4 | 1473 |
| 5 | 14988 |
| 6 | 173007 |
| 7 | 2228544 |
| 8 | 31636449 |
| 9 | 490102164 |
| 10 | 8219695239 |
| 11 | 148262469336 |
| 12 | 2860241078817 |
| 13 | 58736954622492 |
| 14 | 1278727896354687 |
| 15 | 29406849577341552 |
| 16 | 712119108949808193 |
| 17 | 18108134430393657636 |
| 18 | 482306685868464422391 |
| 19 | 13425231879291031821576 |
[1,4,23,168,1473,14988,173007,2228544,31636449, 490102164,8219695239,148262469336,2860241078817, 58736954622492,1278727896354687,29406849577341552, 712119108949808193,18108134430393657636, 482306685868464422391,13425231879291031821576] |