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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 184 |
| 4 | 1704 |
| 5 | 18424 |
| 6 | 227304 |
| 7 | 3147064 |
| 8 | 48278184 |
| 9 | 812387704 |
| 10 | 14872295784 |
| 11 | 294192418744 |
| 12 | 6251984167464 |
| 13 | 142032703137784 |
| 14 | 3434617880825064 |
| 15 | 88075274293319224 |
| 16 | 2387099326339205544 |
| 17 | 68177508876215724664 |
| 18 | 2046501717592969431144 |
| 19 | 64408432189100396344504 |
[1,4,24,184,1704,18424,227304,3147064,48278184, 812387704,14872295784,294192418744,6251984167464, 142032703137784,3434617880825064, 88075274293319224,2387099326339205544, 68177508876215724664,2046501717592969431144, 64408432189100396344504] |