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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 20 |
| 6 | 56 |
| 7 | 182 |
| 8 | 589 |
| 9 | 2088 |
| 10 | 7522 |
| 11 | 28820 |
| 12 | 113092 |
| 13 | 464477 |
| 14 | 1955760 |
| 15 | 8541860 |
| 16 | 38215077 |
| 17 | 176316928 |
| 18 | 832181774 |
| 19 | 4033814912 |
| 20 | 19973824386 |
| 21 | 101257416701 |
| 22 | 523648869394 |
| 23 | 2765873334372 |
| 24 | 14883594433742 |
| 25 | 81646343582385 |
| 26 | 455752361294076 |
| 27 | 2589414185398032 |
[0,1,1,3,7,20,56,182,589,2088,7522,28820,113092, 464477,1955760,8541860,38215077,176316928, 832181774,4033814912,19973824386,101257416701, 523648869394,2765873334372,14883594433742, 81646343582385,455752361294076,2589414185398032] |