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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 15 |
| 3 | 90 |
| 4 | 617 |
| 5 | 4248 |
| 6 | 29945 |
| 7 | 213404 |
| 8 | 1535661 |
| 9 | 11129314 |
| 10 | 81123369 |
| 11 | 594092166 |
| 12 | 4367701295 |
| 13 | 32216566492 |
| 14 | 238301617605 |
| 15 | 1766979857196 |
| 16 | 13129849298327 |
| 17 | 97746629874786 |
| 18 | 728897653778335 |
| 19 | 5443488765350770 |
| 20 | 40706993579981847 |
| 21 | 304779612155116444 |
| 22 | 2284440756129389775 |
| 23 | 17139937071103287600 |
[1,2,15,90,617,4248,29945,213404,1535661,11129314, 81123369,594092166,4367701295,32216566492, 238301617605,1766979857196,13129849298327, 97746629874786,728897653778335,5443488765350770, 40706993579981847,304779612155116444, 2284440756129389775,17139937071103287600] |