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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 16 |
| 4 | 154 |
| 5 | 4584 |
| 6 | 130464 |
| 7 | 3816304 |
| 8 | 123180090 |
| 9 | 4422532004 |
| 10 | 175136909492 |
| 11 | 7585703878304 |
| 12 | 356923128965592 |
| 13 | 18139717839708536 |
| 14 | 990827454743868120 |
| 15 | 57910782633622271952 |
| 16 | 3607453763547725076028 |
| 17 | 238660376246383050751764 |
| 18 | 16714929289459273370819900 |
| 19 | 1235688614706272361317140840 |
| 20 | 96170725583233854961162923028 |
[1,2,6,16,154,4584,130464,3816304,123180090, 4422532004,175136909492,7585703878304, 356923128965592,18139717839708536, 990827454743868120,57910782633622271952, 3607453763547725076028,238660376246383050751764, 16714929289459273370819900, 1235688614706272361317140840, 96170725583233854961162923028] |