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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 14 |
| 3 | 36 |
| 4 | 103 |
| 5 | 248 |
| 6 | 684 |
| 7 | 1624 |
| 8 | 4445 |
| 9 | 10524 |
| 10 | 28762 |
| 11 | 68060 |
| 12 | 185955 |
| 13 | 439984 |
| 14 | 1202072 |
| 15 | 2844144 |
| 16 | 7770361 |
| 17 | 18384884 |
| 18 | 50228454 |
| 19 | 118841812 |
| 20 | 324681887 |
| 21 | 768205608 |
| 22 | 2098776772 |
| 23 | 4965759176 |
| 24 | 13566706389 |
| 25 | 32099171980 |
| 26 | 87696568754 |
| 27 | 207492309516 |
| 28 | 566879531803 |
[1,4,14,36,103,248,684,1624,4445,10524,28762, 68060,185955,439984,1202072,2844144,7770361, 18384884,50228454,118841812,324681887,768205608, 2098776772,4965759176,13566706389,32099171980, 87696568754,207492309516,566879531803] |