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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 13 |
| 4 | 55 |
| 5 | 278 |
| 6 | 1671 |
| 7 | 11699 |
| 8 | 93592 |
| 9 | 842334 |
| 10 | 8423347 |
| 11 | 92656819 |
| 12 | 1111881829 |
| 13 | 14454463785 |
| 14 | 202362492994 |
| 15 | 3035437394920 |
| 16 | 48566998318733 |
| 17 | 825638971418476 |
| 18 | 14861501485532570 |
| 19 | 282368528225118844 |
| 20 | 5647370564502376881 |
[2,4,13,55,278,1671,11699,93592,842334,8423347, 92656819,1111881829,14454463785,202362492994, 3035437394920,48566998318733,825638971418476, 14861501485532570,282368528225118844, 5647370564502376881] |