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| n | a(n) |
|---|---|
| -1 | 1 |
| 0 | 2 |
| 1 | 4 |
| 2 | 10 |
| 3 | 28 |
| 4 | 76 |
| 5 | 206 |
| 6 | 561 |
| 7 | 1524 |
| 8 | 4143 |
| 9 | 11261 |
| 10 | 30611 |
| 11 | 83210 |
| 12 | 226188 |
| 13 | 614843 |
| 14 | 1671317 |
| 15 | 4543110 |
| 16 | 12349453 |
| 17 | 33569293 |
| 18 | 91250800 |
| 19 | 248045393 |
| 20 | 674257283 |
| 21 | 1832821321 |
| 22 | 4982124892 |
| 23 | 13542819562 |
| 24 | 36813200321 |
| 25 | 100068653479 |
| 26 | 272014802350 |
| 27 | 739412894299 |
| 28 | 2009932634301 |
[1,2,4,10,28,76,206,561,1524,4143,11261,30611, 83210,226188,614843,1671317,4543110,12349453, 33569293,91250800,248045393,674257283,1832821321, 4982124892,13542819562,36813200321,100068653479, 272014802350,739412894299,2009932634301] |