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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 28 |
| 3 | 166 |
| 4 | 1015 |
| 5 | 6324 |
| 6 | 39901 |
| 7 | 254035 |
| 8 | 1628380 |
| 9 | 10493680 |
| 10 | 67914088 |
| 11 | 441086947 |
| 12 | 2873255906 |
| 13 | 18763759019 |
| 14 | 122803467241 |
| 15 | 805241108334 |
| 16 | 5288922607095 |
| 17 | 34789875710568 |
| 18 | 229147231044397 |
| 19 | 1511104857207706 |
| 20 | 9975701630282920 |
| 21 | 65920216186587257 |
[1,5,28,166,1015,6324,39901,254035,1628380, 10493680,67914088,441086947,2873255906, 18763759019,122803467241,805241108334, 5288922607095,34789875710568,229147231044397, 1511104857207706,9975701630282920, 65920216186587257] |