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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 20 |
| 4 | 72 |
| 5 | 124 |
| 6 | 356 |
| 7 | 664 |
| 8 | 1808 |
| 9 | 3572 |
| 10 | 9148 |
| 11 | 19040 |
| 12 | 46784 |
| 13 | 100412 |
| 14 | 240716 |
| 15 | 527128 |
| 16 | 1242560 |
| 17 | 2758676 |
| 18 | 6430140 |
| 19 | 14405648 |
| 20 | 33331296 |
| 21 | 75121004 |
| 22 | 172964748 |
| 23 | 391375112 |
| 24 | 898217344 |
| 25 | 2037797060 |
| 26 | 4666779068 |
| 27 | 10606071296 |
| 28 | 24254561056 |
| 29 | 55186525212 |
[4,16,20,72,124,356,664,1808,3572,9148,19040, 46784,100412,240716,527128,1242560,2758676, 6430140,14405648,33331296,75121004,172964748, 391375112,898217344,2037797060,4666779068, 10606071296,24254561056,55186525212] |