The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 20 |
| 2 | 140 |
| 3 | 700 |
| 4 | 1540 |
| 5 | 17500 |
| 6 | 7700 |
| 7 | 122500 |
| 8 | 26180 |
| 9 | 53900 |
| 10 | 192500 |
| 11 | 7035875 |
| 12 | 130900 |
| 13 | 592900 |
| 14 | 4812500 |
| 15 | 1347500 |
| 16 | 602140 |
| 17 | 150062500 |
| 18 | 916300 |
[0,20,140,700,1540,17500,7700,122500,26180,53900, 192500,7035875,130900,592900,4812500,1347500, 602140,150062500,916300] |