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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 9 |
| 3 | 42 |
| 4 | 152 |
| 5 | 480 |
| 6 | 1392 |
| 7 | 3808 |
| 8 | 9984 |
| 9 | 25344 |
| 10 | 62720 |
| 11 | 152064 |
| 12 | 362496 |
| 13 | 851968 |
| 14 | 1978368 |
| 15 | 4546560 |
| 16 | 10354688 |
| 17 | 23396352 |
| 18 | 52494336 |
| 19 | 117047296 |
| 20 | 259522560 |
| 21 | 572522496 |
| 22 | 1257242624 |
| 23 | 2749366272 |
| 24 | 5989466112 |
| 25 | 13002342400 |
| 26 | 28135391232 |
[0,1,9,42,152,480,1392,3808,9984,25344,62720, 152064,362496,851968,1978368,4546560,10354688, 23396352,52494336,117047296,259522560,572522496, 1257242624,2749366272,5989466112,13002342400, 28135391232] |