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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 17 |
| 5 | 120 |
| 6 | 915 |
| 7 | 9470 |
| 8 | 104436 |
| 9 | 1432713 |
| 10 | 20709209 |
| 11 | 354493902 |
| 12 | 6343919118 |
| 13 | 130255212146 |
| 14 | 2780356513594 |
| 15 | 66607482974307 |
| 16 | 1651884203936474 |
| 17 | 45240390673466869 |
| 18 | 1278413274487999471 |
| 19 | 39403978336643657797 |
| 20 | 1249821733374560346851 |
| 21 | 42820844948653526713511 |
[1,1,1,4,17,120,915,9470,104436,1432713,20709209, 354493902,6343919118,130255212146,2780356513594, 66607482974307,1651884203936474,45240390673466869, 1278413274487999471,39403978336643657797, 1249821733374560346851,42820844948653526713511] |