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Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 20 |
| 3 | 100 |
| 4 | 496 |
| 5 | 2464 |
| 6 | 12240 |
| 7 | 60800 |
| 8 | 302016 |
| 9 | 1500224 |
| 10 | 7452160 |
| 11 | 37017600 |
| 12 | 183879936 |
| 13 | 913398784 |
| 14 | 4537185280 |
| 15 | 22537856000 |
| 16 | 111953760256 |
| 17 | 556115206144 |
| 18 | 2762427289600 |
| 19 | 13721985024000 |
| 20 | 68162110078976 |
| 21 | 338586089570304 |
[1,4,20,100,496,2464,12240,60800,302016,1500224, 7452160,37017600,183879936,913398784,4537185280, 22537856000,111953760256,556115206144, 2762427289600,13721985024000,68162110078976, 338586089570304] |