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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 9 |
| 6 | 28 |
| 7 | 81 |
| 8 | 232 |
| 9 | 673 |
| 10 | 1944 |
| 11 | 5617 |
| 12 | 16236 |
| 13 | 46921 |
| 14 | 135604 |
| 15 | 391905 |
| 16 | 1132624 |
| 17 | 3273345 |
| 18 | 9460144 |
| 19 | 27340321 |
| 20 | 79014996 |
| 21 | 228357577 |
| 22 | 659965644 |
| 23 | 1907336113 |
| 24 | 5512303672 |
| 25 | 15930853281 |
| 26 | 46041020488 |
| 27 | 133061018769 |
| 28 | 384553481404 |
| 29 | 1111380188041 |
[0,1,0,1,4,9,28,81,232,673,1944,5617,16236,46921, 135604,391905,1132624,3273345,9460144,27340321, 79014996,228357577,659965644,1907336113, 5512303672,15930853281,46041020488,133061018769, 384553481404,1111380188041] |