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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 37 |
| 5 | 101 |
| 6 | 269 |
| 7 | 710 |
| 8 | 1865 |
| 9 | 4890 |
| 10 | 12810 |
| 11 | 33546 |
| 12 | 87834 |
| 13 | 229963 |
| 14 | 602062 |
| 15 | 1576231 |
| 16 | 4126639 |
| 17 | 10803695 |
| 18 | 28284455 |
| 19 | 74049680 |
| 20 | 193864595 |
| 21 | 507544116 |
| 22 | 1328767764 |
| 23 | 3478759188 |
| 24 | 9107509812 |
| 25 | 23843770261 |
| 26 | 62423800984 |
| 27 | 163427632705 |
[0,1,4,13,37,101,269,710,1865,4890,12810,33546, 87834,229963,602062,1576231,4126639,10803695, 28284455,74049680,193864595,507544116,1328767764, 3478759188,9107509812,23843770261,62423800984, 163427632705] |