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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 195 |
| 5 | 2046 |
| 6 | 26752 |
| 7 | 422546 |
| 8 | 7849611 |
| 9 | 167781117 |
| 10 | 4054557471 |
| 11 | 109246333917 |
| 12 | 3245641491658 |
| 13 | 105366022410057 |
| 14 | 3709933487122164 |
| 15 | 140791348680766521 |
| 16 | 5728108758307500165 |
| 17 | 248696925989154108462 |
| 18 | 11476424805495560002162 |
| 19 | 560894026563924188981599 |
| 20 | 28941826672247857117927894 |
[1,1,4,24,195,2046,26752,422546,7849611,167781117, 4054557471,109246333917,3245641491658, 105366022410057,3709933487122164, 140791348680766521,5728108758307500165, 248696925989154108462,11476424805495560002162, 560894026563924188981599, 28941826672247857117927894] |