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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 23 |
| 6 | 73 |
| 7 | 261 |
| 8 | 916 |
| 9 | 3370 |
| 10 | 12418 |
| 11 | 46527 |
| 12 | 174991 |
| 13 | 663380 |
| 14 | 2524605 |
| 15 | 9652679 |
| 16 | 37028654 |
| 17 | 142514143 |
| 18 | 550002180 |
| 19 | 2128047718 |
| 20 | 8252388728 |
| 21 | 32068797010 |
| 22 | 124855150040 |
| 23 | 486952692675 |
| 24 | 1902227344361 |
| 25 | 7441861777311 |
| 26 | 29153922116412 |
| 27 | 114358089656116 |
[0,0,1,3,7,23,73,261,916,3370,12418,46527,174991, 663380,2524605,9652679,37028654,142514143, 550002180,2128047718,8252388728,32068797010, 124855150040,486952692675,1902227344361, 7441861777311,29153922116412,114358089656116] |