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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 0 |
| 4 | 3 |
| 5 | 1 |
| 6 | 7 |
| 7 | 18 |
| 8 | 52 |
| 9 | 144 |
| 10 | 405 |
| 11 | 1124 |
| 12 | 3113 |
| 13 | 8688 |
| 14 | 24346 |
| 15 | 68385 |
| 16 | 192524 |
| 17 | 542537 |
| 18 | 1529960 |
| 19 | 4316175 |
| 20 | 12178973 |
| 21 | 34370746 |
| 22 | 97008377 |
| 23 | 273813995 |
| 24 | 772895361 |
| 25 | 2181712563 |
| 26 | 6158599574 |
| 27 | 17384869895 |
| 28 | 49075425772 |
| 29 | 138534755824 |
| 30 | 391070202040 |
[0,3,0,3,1,7,18,52,144,405,1124,3113,8688,24346, 68385,192524,542537,1529960,4316175,12178973, 34370746,97008377,273813995,772895361,2181712563, 6158599574,17384869895,49075425772,138534755824, 391070202040] |