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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 51 |
| 5 | 170 |
| 6 | 767 |
| 7 | 2865 |
| 8 | 13303 |
| 9 | 52106 |
| 10 | 246262 |
| 11 | 999415 |
| 12 | 4781050 |
| 13 | 19881284 |
| 14 | 95906783 |
| 15 | 406016883 |
| 16 | 1970864990 |
| 17 | 8460785652 |
| 18 | 41264143733 |
| 19 | 179101755477 |
| 20 | 876723078894 |
| 21 | 3839561286219 |
| 22 | 18850403902895 |
| 23 | 83169160694236 |
| 24 | 409293995669836 |
| 25 | 1817149685976593 |
| 26 | 8960144246683395 |
| 27 | 39993339632768805 |
[1,1,4,12,51,170,767,2865,13303,52106,246262, 999415,4781050,19881284,95906783,406016883, 1970864990,8460785652,41264143733,179101755477, 876723078894,3839561286219,18850403902895, 83169160694236,409293995669836,1817149685976593, 8960144246683395,39993339632768805] |