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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 52 |
| 6 | 288 |
| 7 | 1871 |
| 8 | 14034 |
| 9 | 119292 |
| 10 | 1133278 |
| 11 | 11899423 |
| 12 | 136843365 |
| 13 | 1710542068 |
| 14 | 23092317922 |
| 15 | 334838609874 |
| 16 | 5189998453040 |
| 17 | 85634974475162 |
| 18 | 1498612053315336 |
| 19 | 27724322986333718 |
| 20 | 540624298233507504 |
[2,1,1,3,12,52,288,1871,14034,119292,1133278, 11899423,136843365,1710542068,23092317922, 334838609874,5189998453040,85634974475162, 1498612053315336,27724322986333718, 540624298233507504] |