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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 16 |
| 3 | 52 |
| 4 | 160 |
| 5 | 484 |
| 6 | 1456 |
| 7 | 4372 |
| 8 | 13120 |
| 9 | 39364 |
| 10 | 118096 |
| 11 | 354292 |
| 12 | 1062880 |
| 13 | 3188644 |
| 14 | 9565936 |
| 15 | 28697812 |
| 16 | 86093440 |
| 17 | 258280324 |
| 18 | 774840976 |
| 19 | 2324522932 |
| 20 | 6973568800 |
| 21 | 20920706404 |
| 22 | 62762119216 |
| 23 | 188286357652 |
| 24 | 564859072960 |
| 25 | 1694577218884 |
[0,4,16,52,160,484,1456,4372,13120,39364,118096, 354292,1062880,3188644,9565936,28697812,86093440, 258280324,774840976,2324522932,6973568800, 20920706404,62762119216,188286357652,564859072960, 1694577218884] |