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Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 20 |
| 6 | 160 |
| 7 | 1240 |
| 8 | 13560 |
| 9 | 149900 |
| 10 | 2011940 |
| 11 | 28865620 |
| 12 | 475287860 |
| 13 | 8289874060 |
| 14 | 161736893240 |
| 15 | 3350194920540 |
| 16 | 75447930411100 |
| 17 | 1807230749404340 |
| 18 | 46377810638160560 |
| 19 | 1258317734014917940 |
[1,1,1,4,20,160,1240,13560,149900,2011940, 28865620,475287860,8289874060,161736893240, 3350194920540,75447930411100,1807230749404340, 46377810638160560,1258317734014917940] |