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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 116 |
| 5 | 901 |
| 6 | 8422 |
| 7 | 89755 |
| 8 | 1061048 |
| 9 | 13746169 |
| 10 | 193901066 |
| 11 | 2965146559 |
| 12 | 48946004956 |
| 13 | 867463969789 |
| 14 | 16405240966766 |
| 15 | 329147315037811 |
| 16 | 6973157545554128 |
| 17 | 155446026607476145 |
| 18 | 3636697161715448914 |
| 19 | 89099916704329731895 |
| 20 | 2281451214192505136516 |
[1,1,4,19,116,901,8422,89755,1061048,13746169, 193901066,2965146559,48946004956,867463969789, 16405240966766,329147315037811,6973157545554128, 155446026607476145,3636697161715448914, 89099916704329731895,2281451214192505136516] |