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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 52 |
| 4 | 156 |
| 5 | 428 |
| 6 | 1120 |
| 7 | 2772 |
| 8 | 6616 |
| 9 | 15224 |
| 10 | 34032 |
| 11 | 74020 |
| 12 | 157340 |
| 13 | 327244 |
| 14 | 667824 |
| 15 | 1338828 |
| 16 | 2641332 |
| 17 | 5133372 |
| 18 | 9840432 |
| 19 | 18621476 |
| 20 | 34818852 |
| 21 | 64374564 |
| 22 | 117768176 |
| 23 | 213306948 |
| 24 | 382733816 |
| 25 | 680630120 |
| 26 | 1200198784 |
| 27 | 2099417544 |
| 28 | 3644332860 |
| 29 | 6280017740 |
| 30 | 10746594208 |
[1,4,16,52,156,428,1120,2772,6616,15224,34032, 74020,157340,327244,667824,1338828,2641332, 5133372,9840432,18621476,34818852,64374564, 117768176,213306948,382733816,680630120, 1200198784,2099417544,3644332860,6280017740, 10746594208] |