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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 63 |
| 5 | 226 |
| 6 | 870 |
| 7 | 3365 |
| 8 | 13697 |
| 9 | 55917 |
| 10 | 235493 |
| 11 | 991616 |
| 12 | 4287439 |
| 13 | 18531073 |
| 14 | 81564725 |
| 15 | 358571572 |
| 16 | 1602215627 |
| 17 | 7152092988 |
| 18 | 32311542880 |
| 19 | 145790688544 |
| 20 | 665088946686 |
| 21 | 3031019012280 |
| 22 | 13931089053070 |
| 23 | 63959612298966 |
| 24 | 295972677188241 |
| 25 | 1368411197961976 |
| 26 | 6366687361131662 |
| 27 | 29595489020917756 |
[1,2,6,18,63,226,870,3365,13697,55917,235493, 991616,4287439,18531073,81564725,358571572, 1602215627,7152092988,32311542880,145790688544, 665088946686,3031019012280,13931089053070, 63959612298966,295972677188241,1368411197961976, 6366687361131662,29595489020917756] |