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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 32 |
| 6 | 92 |
| 7 | 264 |
| 8 | 756 |
| 9 | 2176 |
| 10 | 6252 |
| 11 | 17976 |
| 12 | 51684 |
| 13 | 148592 |
| 14 | 427228 |
| 15 | 1228328 |
| 16 | 3531604 |
| 17 | 10153824 |
| 18 | 29193548 |
| 19 | 83935256 |
| 20 | 241324740 |
| 21 | 693839952 |
| 22 | 1994879932 |
| 23 | 5735538696 |
| 24 | 16490418228 |
| 25 | 47412092736 |
| 26 | 136315920428 |
| 27 | 391925964280 |
[1,2,4,12,32,92,264,756,2176,6252,17976,51684, 148592,427228,1228328,3531604,10153824,29193548, 83935256,241324740,693839952,1994879932, 5735538696,16490418228,47412092736,136315920428, 391925964280] |