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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 32 |
| 3 | 232 |
| 4 | 1690 |
| 5 | 12340 |
| 6 | 90112 |
| 7 | 658204 |
| 8 | 4807732 |
| 9 | 35118024 |
| 10 | 256519346 |
| 11 | 1873747524 |
| 12 | 13686804048 |
| 13 | 99975389852 |
| 14 | 730271188300 |
| 15 | 5334272943080 |
| 16 | 38964248230442 |
| 17 | 284614727917460 |
| 18 | 2078971032009920 |
| 19 | 15185864006789660 |
| 20 | 110925290484682724 |
[4,32,232,1690,12340,90112,658204,4807732, 35118024,256519346,1873747524,13686804048, 99975389852,730271188300,5334272943080, 38964248230442,284614727917460,2078971032009920, 15185864006789660,110925290484682724] |