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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 72 |
| 5 | 290 |
| 6 | 1160 |
| 7 | 4642 |
| 8 | 18568 |
| 9 | 74274 |
| 10 | 297096 |
| 11 | 1188386 |
| 12 | 4753544 |
| 13 | 19014178 |
| 14 | 76056712 |
| 15 | 304226850 |
| 16 | 1216907400 |
| 17 | 4867629602 |
| 18 | 19470518408 |
| 19 | 77882073634 |
| 20 | 311528294536 |
| 21 | 1246113178146 |
| 22 | 4984452712584 |
| 23 | 19937810850338 |
| 24 | 79751243401352 |
[0,1,4,18,72,290,1160,4642,18568,74274,297096, 1188386,4753544,19014178,76056712,304226850, 1216907400,4867629602,19470518408,77882073634, 311528294536,1246113178146,4984452712584, 19937810850338,79751243401352] |