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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 150 |
| 5 | 1512 |
| 6 | 19208 |
| 7 | 294912 |
| 8 | 5314410 |
| 9 | 110000000 |
| 10 | 2572306572 |
| 11 | 67077144576 |
| 12 | 1930018885886 |
| 13 | 60743477544960 |
| 14 | 2075941406250000 |
| 15 | 76561193665298432 |
| 16 | 3030800878069216722 |
| 17 | 128186171713071710208 |
| 18 | 5768828271352423353620 |
| 19 | 275251200000000000000000 |
| 20 | 13879377432727741655370342 |
[2,1,4,20,150,1512,19208,294912,5314410,110000000, 2572306572,67077144576,1930018885886, 60743477544960,2075941406250000,76561193665298432, 3030800878069216722,128186171713071710208, 5768828271352423353620,275251200000000000000000, 13879377432727741655370342] |