The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 180 |
| 6 | 1476 |
| 7 | 14728 |
| 8 | 173216 |
| 9 | 2346480 |
| 10 | 35981200 |
| 11 | 616111056 |
| 12 | 11652662880 |
| 13 | 241259095168 |
| 14 | 5427319729664 |
| 15 | 131818482923520 |
| 16 | 3437894427590656 |
| 17 | 95825936705566464 |
| 18 | 2842834581982211328 |
| 19 | 89435890422890433280 |
| 20 | 2974081497762693670400 |
| 21 | 104234511362034627442176 |
[1,2,6,28,180,1476,14728,173216,2346480,35981200, 616111056,11652662880,241259095168,5427319729664, 131818482923520,3437894427590656, 95825936705566464,2842834581982211328, 89435890422890433280,2974081497762693670400, 104234511362034627442176] |