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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 23 |
| 3 | 121 |
| 4 | 617 |
| 5 | 3109 |
| 6 | 15593 |
| 7 | 78061 |
| 8 | 390497 |
| 9 | 1952869 |
| 10 | 9765113 |
| 11 | 48827101 |
| 12 | 244138577 |
| 13 | 1220699029 |
| 14 | 6103507433 |
| 15 | 30517561741 |
| 16 | 152587857857 |
| 17 | 762939387589 |
| 18 | 3814697134553 |
| 19 | 19073486065981 |
| 20 | 95367431116337 |
[1,4,23,121,617,3109,15593,78061,390497,1952869, 9765113,48827101,244138577,1220699029,6103507433, 30517561741,152587857857,762939387589, 3814697134553,19073486065981,95367431116337] |