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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 21 |
| 3 | 161 |
| 4 | 728 |
| 5 | 2415 |
| 6 | 6538 |
| 7 | 15330 |
| 8 | 32292 |
| 9 | 62601 |
| 10 | 113575 |
| 11 | 195195 |
| 12 | 320684 |
| 13 | 507143 |
| 14 | 776244 |
| 15 | 1154980 |
| 16 | 1676472 |
| 17 | 2380833 |
| 18 | 3316089 |
| 19 | 4539157 |
| 20 | 6116880 |
| 21 | 8127119 |
| 22 | 10659902 |
| 23 | 13818630 |
| 24 | 17721340 |
| 25 | 22502025 |
| 26 | 28312011 |
| 27 | 35321391 |
| 28 | 43720516 |
[0,1,21,161,728,2415,6538,15330,32292,62601, 113575,195195,320684,507143,776244,1154980, 1676472,2380833,3316089,4539157,6116880,8127119, 10659902,13818630,17721340,22502025,28312011, 35321391,43720516] |