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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 6 |
| 5 | 20 |
| 6 | 70 |
| 7 | 196 |
| 8 | 542 |
| 9 | 1396 |
| 10 | 3526 |
| 11 | 8628 |
| 12 | 20766 |
| 13 | 49092 |
| 14 | 114598 |
| 15 | 264356 |
| 16 | 603998 |
| 17 | 1368148 |
| 18 | 3076166 |
| 19 | 6870740 |
| 20 | 15256158 |
| 21 | 33696804 |
| 22 | 74073510 |
| 23 | 162127940 |
| 24 | 353460766 |
| 25 | 767816500 |
| 26 | 1662394310 |
| 27 | 3588252916 |
| 28 | 7723318942 |
| 29 | 16580031876 |
| 30 | 35506388646 |
| 31 | 75864499428 |
[0,0,0,0,6,20,70,196,542,1396,3526,8628,20766, 49092,114598,264356,603998,1368148,3076166, 6870740,15256158,33696804,74073510,162127940, 353460766,767816500,1662394310,3588252916, 7723318942,16580031876,35506388646,75864499428] |