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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 14 |
| 3 | 48 |
| 4 | 164 |
| 5 | 560 |
| 6 | 1912 |
| 7 | 6528 |
| 8 | 22288 |
| 9 | 76096 |
| 10 | 259808 |
| 11 | 887040 |
| 12 | 3028544 |
| 13 | 10340096 |
| 14 | 35303296 |
| 15 | 120532992 |
| 16 | 411525376 |
| 17 | 1405035520 |
| 18 | 4797091328 |
| 19 | 16378294272 |
| 20 | 55918994432 |
| 21 | 190919389184 |
| 22 | 651839567872 |
| 23 | 2225519493120 |
| 24 | 7598398836736 |
| 25 | 25942556360704 |
| 26 | 88573427769344 |
| 27 | 302408598355968 |
[1,4,14,48,164,560,1912,6528,22288,76096,259808, 887040,3028544,10340096,35303296,120532992, 411525376,1405035520,4797091328,16378294272, 55918994432,190919389184,651839567872, 2225519493120,7598398836736,25942556360704, 88573427769344,302408598355968] |