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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 480 |
| 6 | 5094 |
| 7 | 65534 |
| 8 | 984808 |
| 9 | 16992144 |
| 10 | 327038880 |
| 11 | 6951172272 |
| 12 | 160900135032 |
| 13 | 4030551570864 |
| 14 | 108477114581640 |
| 15 | 3122444423175240 |
| 16 | 95686679702270784 |
| 17 | 3110711057099693568 |
| 18 | 106921473349790826432 |
| 19 | 3874480434910990168128 |
| 20 | 147622208056015906586880 |
[1,1,2,9,56,480,5094,65534,984808,16992144, 327038880,6951172272,160900135032,4030551570864, 108477114581640,3122444423175240, 95686679702270784,3110711057099693568, 106921473349790826432,3874480434910990168128, 147622208056015906586880] |